Steps to reproduce: 1. Run ``` expiry_date='2020-09-10T00:00:00' acls='package_push,package_release,package_access' snap_name='firefox' snapcraft export-login --channels=esr --snaps="snap_name" --acls="$acls" --expires="$esr_macaroon_file ``` (Note there's a bug in the last command, "snap_name" instead of "$snap_name". 2. Fill the right credentials. Expected results: A meaningful error message like: "Server reported 'snap_name' is not a valid snap". Actual results: Just this error message is provided: "Authentication error: Failed to get macaroon". Context: I made this mistake after 2 successful macaroon exports. The lack of information lead me to think there was a bug around custom tracks. "ESR" was created in https://forum.snapcraft.io/t/firefox-please-create-the-track-esr/5006. I ended up filing a bug against the server: https://bugs.launchpad.net/firefox/+bug/1843275. Kudos to Daniel Manrique who gave me a simple way to debug what's happening. Although, I think error messages should provide more info by default.