diff --git a/Website/main.py b/Website/main.py
index ae17c75..7bcd3ec 100644
--- a/Website/main.py
+++ b/Website/main.py
@@ -2076,10 +2076,22 @@ def booking_payment():
             # Do NOT create an invoice directly. Instead request provisioning via server_steering
             booking_number = f"BOOK-{datetime.utcnow().strftime('%Y%m%d%H%M%S')}"
 
-            # Build a subdomain from the school name (fallback to username) and ensure uniqueness
-            base = _slugify_subdomain(form_data.get("school_name") or session.get("username") or booking_number)
-            subdomain = f"{base}-{datetime.utcnow().strftime('%Y%m%d%H%M%S')}"
-            subdomain = subdomain[:63]
+            # Build a subdomain from the school name (fallback to username)
+            # Use lowercase, sanitized school name and check for existing instances.
+            raw_base = form_data.get("school_name") or session.get("username") or booking_number
+            base = _slugify_subdomain(raw_base).lower()[:51]
+
+            # Check existing instances and require the user to choose a different name on conflict
+            try:
+                existing = steering.instace.list() or []
+            except Exception:
+                existing = []
+
+            if base in existing:
+                flash("Die gewünschte Subdomain (aus dem Schulnamen) existiert bereits. Bitte wähle einen anderen Schulnamen.", "error")
+                return render_template("schnell_buchung.html", **review_data)
+
+            subdomain = base[:63]
 
             provision_status = "not_started"
             provision_port = None
@@ -2141,13 +2153,13 @@ def booking_payment():
                 "source": "booking_payment",
             }
 
-            prov_client = None
+            req_client = None
             try:
-                prov_client, prov_col = _get_collection("provision_requests")
-                prov_col.insert_one(provision_payload)
+                req_client, req_col = _get_collection("instance_requests")
+                req_col.insert_one(provision_payload)
             finally:
-                if prov_client:
-                    prov_client.close()
+                if req_client:
+                    req_client.close()
 
     except PyMongoError:
         flash("Buchungsanfrage konnte nicht gesendet werden.", "error")
@@ -2169,20 +2181,20 @@ def booking_payment():
 
 
 
-@app.route('/provision/delete', methods=['POST'])
+@app.route('/instance_request/delete', methods=['POST'])
 @login_required
-def provision_delete():
+def instance_request_delete():
     prov_id = _sanitize_text(request.form.get("prov_id") or "", 64)
     if not prov_id:
         flash("Ungültige Anfrage.", "error")
         return redirect(url_for("my_invoices"))
 
-    prov_client = None
+    req_client = None
     try:
-        prov_client, prov_col = _get_collection("provision_requests")
-        prov = prov_col.find_one({"_id": ObjectId(prov_id)})
+        req_client, req_col = _get_collection("instance_requests")
+        prov = req_col.find_one({"_id": ObjectId(prov_id)})
         if not prov:
-            flash("Provisionierungsanfrage nicht gefunden.", "error")
+            flash("Instanz-Anfrage nicht gefunden.", "error")
             return redirect(url_for("my_invoices"))
 
         # Only owner or admin can delete
@@ -2190,13 +2202,13 @@ def provision_delete():
             flash("Keine Berechtigung zum Löschen dieser Anfrage.", "error")
             return redirect(url_for("my_invoices"))
 
-        prov_col.delete_one({"_id": prov.get("_id")})
-        flash("Provisionierungsanfrage gelöscht.", "success")
+        req_col.delete_one({"_id": prov.get("_id")})
+        flash("Instanz-Anfrage gelöscht.", "success")
     except Exception:
-        flash("Provisionierungsanfrage konnte nicht gelöscht werden.", "error")
+        flash("Instanz-Anfrage konnte nicht gelöscht werden.", "error")
     finally:
-        if prov_client:
-            prov_client.close()
+        if req_client:
+            req_client.close()
 
     return redirect(url_for("my_invoices"))
 
@@ -2776,19 +2788,19 @@ def my_invoices():
         if client:
             client.close()
 
-    # Load provisioning requests for this user
-    provision_requests = []
+    # Load instance requests for this user
+    instance_requests = []
     try:
-        prov_client, prov_col = _get_collection("provision_requests")
-        provision_requests = list(prov_col.find({"username": session.get("username")}).sort("created_at", -1))
-        for item in provision_requests:
+        req_client, req_col = _get_collection("instance_requests")
+        instance_requests = list(req_col.find({"username": session.get("username")}).sort("created_at", -1))
+        for item in instance_requests:
             item["id"] = str(item.get("_id"))
     except PyMongoError:
-        flash("Provisionierungsanfragen konnten nicht geladen werden.", "error")
+        flash("Instanz-Anfragen konnten nicht geladen werden.", "error")
     finally:
-        if 'prov_client' in locals() and prov_client:
-            prov_client.close()
-    return render_template("my_invoices.html", invoices=invoices, provision_requests=provision_requests)
+        if 'req_client' in locals() and req_client:
+            req_client.close()
+    return render_template("my_invoices.html", invoices=invoices, instance_requests=instance_requests)
 
 
 @app.route('/my/instance', methods=['GET', 'POST'])
@@ -3140,13 +3152,13 @@ def admin_invoices():
                 flash("Rechnung angelegt.", "success")
 
             elif action == "create_from_provision" and prov_id:
-                # Create an invoice from a provision request
-                prov_client = None
+                # Create an invoice from an instance request
+                req_client = None
                 try:
-                    prov_client, prov_col = _get_collection("provision_requests")
-                    prov = prov_col.find_one({"_id": ObjectId(prov_id)})
+                    req_client, req_col = _get_collection("instance_requests")
+                    prov = req_col.find_one({"_id": ObjectId(prov_id)})
                     if not prov:
-                        flash("Provisionierungsanfrage nicht gefunden.", "error")
+                        flash("Instanz-Anfrage nicht gefunden.", "error")
                         return redirect(url_for("admin_invoices"))
 
                     username = prov.get("username") or ""
@@ -3176,35 +3188,35 @@ def admin_invoices():
                         }
                     )
 
-                    prov_col.update_one({"_id": prov.get("_id")}, {"$set": {"provision_status": "invoice_created", "updated_at": _utc_now_iso()}})
-                    flash("Rechnung aus Provisionierungsanfrage erstellt.", "success")
+                    req_col.update_one({"_id": prov.get("_id")}, {"$set": {"provision_status": "invoice_created", "updated_at": _utc_now_iso()}})
+                    flash("Rechnung aus Instanz-Anfrage erstellt.", "success")
                 except Exception:
-                    flash("Fehler beim Erstellen der Rechnung aus Provisionierungsanfrage.", "error")
+                    flash("Fehler beim Erstellen der Rechnung aus Instanz-Anfrage.", "error")
                 finally:
-                    if prov_client:
-                        prov_client.close()
+                    if req_client:
+                        req_client.close()
 
             elif action == "update_provision" and prov_id:
                 # Update provision request status (accept/reject/complete)
                 new_status = _sanitize_text(request.form.get("prov_status") or "", 40)
-                prov_client = None
+                req_client = None
                 try:
-                    prov_client, prov_col = _get_collection("provision_requests")
-                    prov_col.update_one({"_id": ObjectId(prov_id)}, {"$set": {"provision_status": new_status, "updated_at": _utc_now_iso()}})
-                    flash("Provisionierungsanfrage aktualisiert.", "success")
+                    req_client, req_col = _get_collection("instance_requests")
+                    req_col.update_one({"_id": ObjectId(prov_id)}, {"$set": {"provision_status": new_status, "updated_at": _utc_now_iso()}})
+                    flash("Instanz-Anfrage aktualisiert.", "success")
                 except Exception:
-                    flash("Provisionierungsanfrage konnte nicht aktualisiert werden.", "error")
+                    flash("Instanz-Anfrage konnte nicht aktualisiert werden.", "error")
                 finally:
-                    if prov_client:
-                        prov_client.close()
+                    if req_client:
+                        req_client.close()
             elif action in {"run_provision", "retry_provision", "configure_provision"} and prov_id:
                 # Admin-triggered provisioning actions: start/retry/configure
-                prov_client = None
+                req_client = None
                 try:
-                    prov_client, prov_col = _get_collection("provision_requests")
-                    prov = prov_col.find_one({"_id": ObjectId(prov_id)})
+                    req_client, req_col = _get_collection("instance_requests")
+                    prov = req_col.find_one({"_id": ObjectId(prov_id)})
                     if not prov:
-                        flash("Provisionierungsanfrage nicht gefunden.", "error")
+                        flash("Instanz-Anfrage nicht gefunden.", "error")
                         return redirect(url_for("admin_invoices"))
 
                     subdomain = prov.get("subdomain") or _slugify_subdomain(prov.get("booking_data", {}).get("school_name") or prov.get("username") or prov.get("booking_number") or "prov")
@@ -3243,25 +3255,25 @@ def admin_invoices():
                                 provision_config_ok = False
                                 provision_error = str(e)
 
-                    prov_col.update_one({"_id": prov.get("_id")}, {"$set": {"provision_status": provision_status, "provision_port": provision_port or "", "provision_config_ok": provision_config_ok, "provision_error": provision_error, "updated_at": _utc_now_iso()}})
+                    req_col.update_one({"_id": prov.get("_id")}, {"$set": {"provision_status": provision_status, "provision_port": provision_port or "", "provision_config_ok": provision_config_ok, "provision_error": provision_error, "updated_at": _utc_now_iso()}})
                     flash("Provisionierungsaktion ausgeführt.", "success")
                 except Exception as e:
                     flash(f"Provisionierungsaktion fehlgeschlagen: {str(e)}", "error")
                 finally:
-                    if prov_client:
-                        prov_client.close()
+                    if req_client:
+                        req_client.close()
 
-            elif action == "delete_provision" and prov_id:
-                prov_client = None
+            elif action == "delete_instance_request" and prov_id:
+                req_client = None
                 try:
-                    prov_client, prov_col = _get_collection("provision_requests")
-                    prov_col.delete_one({"_id": ObjectId(prov_id)})
-                    flash("Provisionierungsanfrage gelöscht.", "success")
+                    req_client, req_col = _get_collection("instance_requests")
+                    req_col.delete_one({"_id": ObjectId(prov_id)})
+                    flash("Instanz-Anfrage gelöscht.", "success")
                 except Exception:
-                    flash("Provisionierungsanfrage konnte nicht gelöscht werden.", "error")
+                    flash("Instanz-Anfrage konnte nicht gelöscht werden.", "error")
                 finally:
-                    if prov_client:
-                        prov_client.close()
+                    if req_client:
+                        req_client.close()
 
             elif action == "update" and invoice_id:
                 amount_text = _sanitize_text(request.form.get("amount_eur") or "0", 20)
@@ -3315,21 +3327,21 @@ def admin_invoices():
         if client:
             client.close()
 
-    # Load provisioning requests for admin review
-    provision_requests = []
+    # Load instance requests for admin review
+    instance_requests = []
     try:
-        prov_client, prov_col = _get_collection("provision_requests")
-        provision_requests = list(prov_col.find().sort("created_at", -1))
-        for item in provision_requests:
+        req_client, req_col = _get_collection("instance_requests")
+        instance_requests = list(req_col.find().sort("created_at", -1))
+        for item in instance_requests:
             item["id"] = str(item.get("_id"))
     except PyMongoError:
-        flash("Provisionierungsanfragen konnten nicht geladen werden.", "error")
+        flash("Instanz-Anfragen konnten nicht geladen werden.", "error")
     finally:
-        if 'prov_client' in locals() and prov_client:
-            prov_client.close()
+        if 'req_client' in locals() and req_client:
+            req_client.close()
 
     users = _list_users_for_admin()
-    return render_template("admin_invoices.html", invoices=invoices, users=users, provision_requests=provision_requests)
+    return render_template("admin_invoices.html", invoices=invoices, users=users, provision_requests=instance_requests)
 
 
 @app.route('/datenschutz')
@@ -3337,6 +3349,24 @@ def datenschutz():
     return render_template("datenschutz.html")
 
 
+@app.route('/instance_request/check_subdomain', methods=['GET'])
+@login_required
+def check_subdomain():
+    name = (request.values.get('school_name') or '').strip()
+    slug = _slugify_subdomain(name)
+    if not slug:
+        return jsonify({"available": False, "slug": "", "message": "Ungültiger Name für Subdomain."})
+
+    try:
+        existing = steering.instace.list() or []
+    except Exception:
+        existing = []
+
+    if slug in existing:
+        return jsonify({"available": False, "slug": slug, "message": "Subdomain bereits vergeben."})
+    return jsonify({"available": True, "slug": slug, "message": "Subdomain verfügbar."})
+
+
 @app.route('/impressum')
 def impressum():
     return render_template("impressum.html")
diff --git a/Website/templates/admin_invoices.html b/Website/templates/admin_invoices.html
index 1e261cb..62d7a29 100644
--- a/Website/templates/admin_invoices.html
+++ b/Website/templates/admin_invoices.html
@@ -64,7 +64,7 @@
         {% endfor %}
         
         {% if provision_requests %}
-        <h2>Provisionierungsanfragen</h2>
+        <h2>Instanz-Anfragen</h2>
         {% for prov in provision_requests %}
         <article class="entry">
             <h3>{{ prov.booking_number or prov.booking_number }}</h3>
@@ -105,7 +105,7 @@
                 <button type="submit">Konfiguration ausführen</button>
             </form>
             <form method="post" style="display:inline-block; margin-right:0.6rem;">
-                <input type="hidden" name="action" value="delete_provision">
+                <input type="hidden" name="action" value="delete_instance_request">
                 <input type="hidden" name="prov_id" value="{{ prov.id }}">
                 <button type="submit" class="danger">Löschen</button>
             </form>
diff --git a/Website/templates/my_invoices.html b/Website/templates/my_invoices.html
index 94c0f10..73e6645 100644
--- a/Website/templates/my_invoices.html
+++ b/Website/templates/my_invoices.html
@@ -46,8 +46,8 @@
 </section>
 
 <section class="panel">
-    <h2>Provisionierungsanfragen</h2>
-    <p>Hier siehst du den Status deiner angeforderten Instanzen/ Buchungen, die vom Admin geprüft werden.</p>
+    <h2>Instanz-Anfragen</h2>
+    <p>Hier siehst du den Status deiner angeforderten Instanzen/Buchungen, die vom Admin geprüft werden.</p>
 </section>
 
 <section class="table-wrap">
@@ -62,7 +62,7 @@
             </tr>
         </thead>
         <tbody>
-            {% for prov in provision_requests %}
+            {% for prov in instance_requests %}
             <tr>
                 <td>{{ prov.booking_number or prov.booking_number }}</td>
                 <td>{{ prov.package_label or prov.package }}</td>
@@ -70,7 +70,7 @@
                 <td>{{ '%.2f'|format(prov.amount_eur or 0) }} EUR</td>
                 <td>
                     {{ prov.provision_status or 'not_started' }}
-                    <form method="post" action="{{ url_for('provision_delete') }}" style="display:inline-block; margin-left:0.6rem;">
+                    <form method="post" action="{{ url_for('instance_request_delete') }}" style="display:inline-block; margin-left:0.6rem;">
                         <input type="hidden" name="prov_id" value="{{ prov.id }}">
                         <button type="submit" class="danger">Löschen</button>
                     </form>
diff --git a/Website/templates/schnell_buchung.html b/Website/templates/schnell_buchung.html
index 4760d77..8e723c3 100644
--- a/Website/templates/schnell_buchung.html
+++ b/Website/templates/schnell_buchung.html
@@ -208,6 +208,7 @@
                 <div class="booking-review__field">
                     <label for="school_name">Schule/Einrichtung *</label>
                     <input id="school_name" name="school_name" type="text" required maxlength="160" value="{{ form_data.school_name }}">
+                    <div id="school_name_feedback" style="margin-top:0.4rem; font-size:0.9rem; color:#6b6b6b;"></div>
                 </div>
                 <div class="booking-review__field">
                     <label for="contact_email">E-Mail *</label>
@@ -242,10 +243,54 @@
             </div>
 
             <div class="booking-review__actions">
-                <button class="btn" type="submit">{{ confirm_label }}</button>
+                <button id="booking_submit" class="btn" type="submit">{{ confirm_label }}</button>
                 <a class="btn secondary" href="{{ url_for('preise') }}">Zurück zu den Preisen</a>
             </div>
         </form>
     </div>
 </section>
+<script>
+(() => {
+    const input = document.getElementById('school_name');
+    const feedback = document.getElementById('school_name_feedback');
+    const submit = document.getElementById('booking_submit');
+    let timer = null;
+
+    function setFeedback(text, ok) {
+        feedback.textContent = text;
+        feedback.style.color = ok ? '#1b8a3e' : '#b02a37';
+        submit.disabled = !ok;
+    }
+
+    async function check(name) {
+        if (!name || name.trim().length < 3) {
+            feedback.textContent = '';
+            submit.disabled = false;
+            return;
+        }
+        try {
+            const params = new URLSearchParams({ school_name: name });
+            const res = await fetch(`/instance_request/check_subdomain?${params.toString()}`, { credentials: 'same-origin' });
+            if (!res.ok) throw new Error('Netzwerkfehler');
+            const j = await res.json();
+            setFeedback(j.message || (j.available ? 'verfügbar' : 'nicht verfügbar'), !!j.available);
+        } catch (e) {
+            setFeedback('Prüfung fehlgeschlagen (Netzwerk).', false);
+        }
+    }
+
+    if (input) {
+        input.addEventListener('input', (e) => {
+            clearTimeout(timer);
+            const val = e.target.value;
+            timer = setTimeout(() => check(val), 500);
+        });
+
+        // initial check on load
+        if (input.value && input.value.trim()) {
+            check(input.value);
+        }
+    }
+})();
+</script>
 {% endblock %}
\ No newline at end of file