diff --git a/app/controllers/api/go_cardless_controller.rb b/app/controllers/api/go_cardless_controller.rb
index 9183b1945..c30907c46 100644
--- a/app/controllers/api/go_cardless_controller.rb
+++ b/app/controllers/api/go_cardless_controller.rb
@@ -33,7 +33,6 @@ def start_flow
   end
 
   def payment_complete
-    # If one-off payment
     builder.make_transaction(params, session.id)
     render json: {success: builder.success?, params: params}
   end
@@ -48,15 +47,11 @@ def builder
     PaymentProcessor::GoCardless::Transaction
   end
 
-  def client
-    GoCardlessPro::Client.new(
-      access_token: Settings.gocardless.token,
-      environment: Settings.gocardless.environment.to_sym
-    )
-  end
-
   def success_url
-    local_params = URI.parse(request.url).query + "&page_id=#{params[:page_id]}"
+    local_params =  Rack::Utils.parse_query(
+      URI.parse(request.url).query
+    ).merge( params.slice(:page_id) ).to_query
+
     "#{request.base_url}/api/go_cardless/payment_complete?#{local_params}"
   end
 end
diff --git a/spec/controllers/api/go_cardless_controller_spec.rb b/spec/controllers/api/go_cardless_controller_spec.rb
index ad4c3def2..dcac50b96 100644
--- a/spec/controllers/api/go_cardless_controller_spec.rb
+++ b/spec/controllers/api/go_cardless_controller_spec.rb
@@ -14,11 +14,11 @@
       subject
     end
 
-    subject { get :start_flow, foo: 'bar' }
+    subject { get :start_flow, page_id: '1', foo: 'bar' }
 
     it 'instantiates GoCardlessDirector' do
       expect(GoCardlessDirector).to have_received(:new).
-        with('fake_session_id', "http://test.host/api/go_cardless/payment_complete?foo=bar")
+        with('fake_session_id', "http://test.host/api/go_cardless/payment_complete?foo=bar&page_id=1")
     end
 
     it 'redirects' do