changes to the status changes

Website/main.py

@@ -3308,7 +3308,7 @@ def booking_payment():
                 )
                 billing_update = {
                     "package": ",".join(effective_package_keys),
-                    "status": "ready",
+                    "status": reuse_instance.get("status") or "ready",
                     "last_message": (
                         "Ausgewählte Module wurden entfernt. Die bestehende Jahresrechnung bleibt unverändert."
                         if booking_action == "downgrade"
@@ -3323,6 +3323,17 @@ def booking_payment():
                         "payment_status": "pending",
                         "payment_due_at": (date.today() + timedelta(days=PAYMENT_GRACE_DAYS)).isoformat(),
                     })
+                else:
+                    # A downgrade changes only the module configuration. Keep
+                    # the existing billing state and invoice untouched.
+                    for billing_field in (
+                        "billing_state",
+                        "payment_status",
+                        "payment_due_at",
+                        "invoice_id",
+                    ):
+                        if billing_field in reuse_instance:
+                            billing_update[billing_field] = reuse_instance[billing_field]
                 if reuse_instance.get("is_trial"):
                     billing_update.update({
                         "is_trial": False,
@@ -3365,10 +3376,18 @@ def booking_payment():
                     "amount_gross_eur": 0.0 if booking_action == "downgrade" else gross_price,
                     "amount_net_eur": 0.0 if booking_action == "downgrade" else net_price,
                     "booking_flow": booking_flow,
-                    "invoice_id": invoice_id,
+                    "invoice_id": (
+                        reuse_instance.get("invoice_id")
+                        if booking_action == "downgrade"
+                        else invoice_id
+                    ),
                     "subdomain": subdomain,
                     "domain": reuse_instance.get("domain") or f"{subdomain}.invario-software.de",
-                    "payment_due_at": (date.today() + timedelta(days=PAYMENT_GRACE_DAYS)).isoformat(),
+                    "payment_due_at": (
+                        reuse_instance.get("payment_due_at")
+                        if booking_action == "downgrade"
+                        else (date.today() + timedelta(days=PAYMENT_GRACE_DAYS)).isoformat()
+                    ),
                     "avv_version": form_data.get("avv_version"),
                     "legal_consents_accepted_at": form_data.get("legal_consents_accepted_at"),
                     "notes": form_data.get("notes"),