I've been using Google Music Manager for a while (years?) on Ubuntu 16.04 and 18.04 and suddenly today it can't connect. It asks for my login and password, then my password again with a captcha, then an MFA code, then it says "Couldn't connect to Google Play - Check your internet connection and try again" (screenshot below). The "Retry" button has no noticeable effect. I can reach other sites and services on the Internet just fine. I don't have any outbound firewall filters configured.
I tried tips from here and here -- no luck.
Here's a screenshot of the error:
I ran into this issue as well - I had already installed Google MusicManager at some point, and blew it up when I installed an update.
My solution was to COMPLETELY remove it and its configuration. First, removing it completely via apt:
sudo apt-get purge google-musicmanager-beta
Then, tracked down all remaining files that referenced it and removed them, including within my own profile:
cd / find . -iname '*musicmanager*' rm <anything that was found above>
Then I reinstalled, and it came up with initial setup dialogs and worked properly. Note that there have been comments that for people with two-factor auth using the feature to just click "Yes" on the phone doesn't work - I had it send me a text message with an auth code instead and it authenticated just fine.