When signing in, confirm that you are using the correct user information. Clear your internet cache prior to retry. If using the correct information, a one-time passcode should be sent to the email. The OTP may take a few minutes to be sent to email.
*Also, please note there’s a time limit once receiving an OTP code. Once email is received, users have 10 minutes to verify this code to login. Once that time is up, the user will need to receive a new code, as the previous one will be invalid. When first signing in to PowerApps, you may be prompted to set up and verify security questions to confirm your identity.