On the command line I can do any operation (fetch, pull, push) without any problem while using git-credential-manager. Within gitfourchette I always get the following error:

It seems that gitfourchette does not care about the settings in .gitconfig:
[credential]
helper =
helper = /usr/local/bin/git-credential-manager
credentialStore = secretservice
[credential "URL_redacted"]
provider = generic