Sometimes Google experiences problems with their Google login, so I recommend you try
- Delete your cookies (not just cache) and see if that resolves the issue.
- If not resolved, reset application permissions for Focuster via the Google.
- Go to: https://myaccount.google.com/permissions
- Find "Focuster" in the list of applications. Click "Remove Access"
- Try to login to Focuster again
Let us know if either of those steps works for you.