fix(stripe): correcting webhook

backend/Modules/Tipping/Contracts/ITipProcessor.cs

@@ -2,7 +2,7 @@ using Hutopy.Modules.Creators.Contracts;
 
 namespace Hutopy.Modules.Tipping.Contracts;
 
-public interface ITipProcessor
+internal interface ITipProcessor
 {
     Task<TipCheckoutSession> CreateCheckoutSessionAsync(
         Guid tipId,
@@ -10,7 +10,7 @@ public interface ITipProcessor
         decimal amount,
         string currency,
         string message,
-        string successUrl,
-        string cancelUrl,
+        Uri successUrl,
+        Uri cancelUrl,
         CancellationToken ct = default);
 }