Fix configure route

app/views/projects/mattermost/new.html.haml

-= form_for(:create, method: :post, url: configure_namespace_project_mattermost_path(@project.namespace, @project, )) do |f|
+= form_for(:create, method: :post, url: configure_namespace_project_mattermost_index_path(@project.namespace, @project)) do |f|
   = "Team ID"
   = f.text_field(:team_id)
   = f.submit 'Configure', class: 'btn btn-save'
-

config/routes/project.rb

@@ -65,7 +65,7 @@ constraints(ProjectUrlConstrainer.new) do
       end
 
       resources :mattermost, only: [:new] do
-        member do
+        collection do
           post :configure
         end
       end