Unable to add a new custom domain to app engine for server side GTM

[cmz]

I am unable to add a new custom domain to my GCP app engine. When at the initial stage "Select the domain you want to use", my sub-domain, which is verified already in GSC, is not an option that I can select.

If I try "verify a new domain" and then verify my subdomain in GSC, it still does not work. There have been other posts which reference this issue, so it looks like a bug in the platform. 

[Marramirez]

Greetings @cmz,

Check out this public issue tracker. There has been a workaround for the problem by using Cloud CLI. You will be utilizing the gcloud app domain-mappings to view and manage your domain mappings. 

If that doesn't solve your problem, you can open an issue tracker or you can contact Google Cloud Support to further look into your case

Let me know if it helped, thanks!