Which Version of GCM are you using ?
From a command prompt, run git credential-manager version and paste the output.
Which service are you trying to connect to
If AzureDevops Hosted describe your url
If you're using Azure DevOps, can you access the repository in the browser via the same URL?
If you're using Azure DevOps, and the account picker shows more than one identity as you authenticate, check that you selected the same one that has access on the web.
Expected behavior
A clear and concise description of what you expected to happen (or code).
Actual behavior
A clear and concise description of what happens, e.g. exception is thrown, UI freezes
Set the env variables GCM_TRACE=1 and GIT_TRACE=1 and run your git command. Redact any private information and attach the log