Heroku now requires a form of Multi-factor-authentication (MFA), generally with a “TOTP” authenticator app.
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Other free TOTP app options are Microsoft Authenticator (I think phone only, not sure about multi-device sync), and Google Authenticator (not sure). You want to make sure you understand how you will keep access to your TOTP-protected accounts if you lose or change devices! I honesty don’t totally understand the expectations for how this works generally, but I understand Authy multi-device setup.