После привязки к Gmail появилось:
"Sorry, the page you're looking for isn’t here anymore
If you reached this page from another part of todoist.com, please let us know so we can correct our mistake."
Are you sure that you haven't created a Todoist account with this Gmail account in the past? Please try to log int with your Google Account and see if it forwards you to an account.
This issue has now been fixed.