Firebase Custom Domain Verification fails

Sorry I should have been more detailed in my description. I bought a domain (icmd.app) on uniregistry and successfully changed the domain name server to netlify, so far so good. Now I am using firebase for authentication, but the email they are sending is using some ugly link with firebase in the title. There is the option to use your custom domain, when you verify that it is yours. Now Firebase shows you some TXT and CNAME entries that you should add, which I did using the netlify dns panel, but after 1 day Firebase still failed to accept the verification.