diff --git a/app/controllers/api/internal/v1/mailers_controller.rb b/app/controllers/api/internal/v1/mailers_controller.rb
index 8bfbe44a16..61035ea244 100644
--- a/app/controllers/api/internal/v1/mailers_controller.rb
+++ b/app/controllers/api/internal/v1/mailers_controller.rb
@@ -13,7 +13,7 @@ def registration
     requesting_user = params.require(:current_user)
     registration_competition = params.require(:competition_id)
     user = User.find(registration_user)
-    registration = user.microservice_registrations.find_by(competition_id: registration_competition)
+    registration = user.find_ms_registration_by(competition_id: registration_competition)
 
     if registration_status == 'pending' && registration_action == 'create'
       RegistrationsMailer.notify_organizers_of_new_registration(registration).deliver_later
diff --git a/app/controllers/api/internal/v1/payment_controller.rb b/app/controllers/api/internal/v1/payment_controller.rb
index e48b4711ef..94d1a43942 100644
--- a/app/controllers/api/internal/v1/payment_controller.rb
+++ b/app/controllers/api/internal/v1/payment_controller.rb
@@ -17,9 +17,7 @@ def init_stripe
     competition = Competition.find(competition_id)
     return render json: { error: "Competition not found" }, status: :not_found unless competition.present?
 
-    ms_registration = competition.microservice_registrations
-                                 .includes(:competition, :user)
-                                 .find_by(user_id: registering_user_id)
+    ms_registration = competition.find_ms_registration_by(user_id: registering_user_id)
 
     return render json: { error: "Registration not found" }, status: :not_found unless ms_registration.present?
 
diff --git a/app/models/concerns/microservice_registration_holder.rb b/app/models/concerns/microservice_registration_holder.rb
index 1db2d54b8e..1c35ca3891 100644
--- a/app/models/concerns/microservice_registration_holder.rb
+++ b/app/models/concerns/microservice_registration_holder.rb
@@ -42,4 +42,21 @@ def microservice_registrations
       end
     end
   end
+
+  private def scoped_find_by(scope, **kwargs)
+    kwarg_symbols = kwargs.keys.map(&:to_sym)
+    own_assoc_key = self.class.model_name.element.to_sym
+
+    preload_keys = MicroserviceRegistration.reflect_on_all_associations.filter { |assoc|
+      # Pick by either the name (ie. `competition`) or the foreign key (ie. `competition_id`) of the association
+      kwarg_symbols.include?(assoc.name.to_sym) || kwargs.keys.include?(assoc.foreign_key.to_sym)
+    }.map(&:name)
+
+    scope.includes(own_assoc_key, *preload_keys)
+         .find_by(own_assoc_key => self, **kwargs)
+  end
+
+  def find_ms_registration_by(**)
+    self.scoped_find_by(MicroserviceRegistration, **) || self.scoped_find_by(self.microservice_registrations, **)
+  end
 end