google cloud platform – Cannot add own domain to app hosted on GCloud App Engine

As my title says i have problem adding my custom domain to app hosted on Google Cloud App Engine.
When i go to my app click on settings -> custom domain -> Add custom domain, I see option “You have no verified domains, to continue submit your domain for verification. Then when i insert my domain it moves me to other window, to insert my domain once again for verification. The problem is when i insert my domain which is already verified i see pop up with green background and message “Automatically verified ownership, verification method: Domain name provider”, then i can press button “Done” which does nothing and button “Go to service” which redirects me to page of Google search console where i can see data of my domain, but still i cannot add this domain to my App Engine app.

I tried waiting but I have been waiting for almost 3 days already and nothing is changed still. My domain is with .pl