Use your @matsprogram.org account if you have one, otherwise a google-auth enabled account. If you don't have a google-auth enabled account registered with MATS then you can ask Nathan Helm-Burger on slack to register one for you, or add Google Auth to your known account.
Sign-in requires a Google account on your email. Two fixes:
Add Google to your email (no Gmail needed)
Go to accounts.google.com/signup → Use your existing email instead → confirm the code Google sends you. Then sign in here as normal.
Use a different email
Already have one with Google (e.g. personal Gmail)? Slack Nathan Helm-Burger and he'll link it to your dashboard account.