fix: gate PayKilla by minimum payment amount

backend/bot/app/web/webapp/billing.py

@@ -1052,6 +1052,22 @@ async def _create_subscription_payment(
                 "unsupported_currency",
                 "Payment method does not support this currency",
             )
+        if not provider_spec.is_usable_for_payment_amount(
+            settings,
+            payment_currency,
+            price,
+        ):
+            logger.warning(
+                "WebApp payment method does not support amount: method=%s amount=%s currency=%s",
+                method,
+                price,
+                payment_currency,
+            )
+            return _json_error(
+                400,
+                "payment_amount_below_minimum",
+                "Payment amount is below the provider minimum",
+            )
         return await provider_spec.create_webapp_payment(
             WebAppPaymentContext(
                 request=request,

backend/bot/app/web/webapp/serializers.py

@@ -943,13 +943,15 @@ def _serialize_payment_methods(
             and spec.is_usable_for_payment_currency(settings, payment_currency)
         ):
             presentation = resolve_provider_presentation(spec, settings, language=lang)
-            methods.append(
-                {
-                    "id": method,
-                    "name": presentation.webapp_label,
-                    "icon": presentation.webapp_icon,
-                }
-            )
+            payload = {
+                "id": method,
+                "name": presentation.webapp_label,
+                "icon": presentation.webapp_icon,
+            }
+            minimum = spec.payment_minimum(settings, payment_currency)
+            if minimum:
+                payload.update(minimum)
+            methods.append(payload)
     return methods