If you could previously sign into the heroku command line interface with heroku login but now you get IP address mismatch error, this is how you can resolve this:

Use the commands heroku login -i  in your terminal. If you have authorization token attached to your account you will face the error:  Your account has MFA enabled; API requests using basic authentication with email and password are not » supported. Please generate an authorization token for API access.

If you have authorization token attached to your account follow these steps:

• Navigate to  Heroku API Authorizations  and create  Heroku CLI Authorization.
• In Authorizations click on create authorization button.
• Add description in pop up eg.sign in with Heroku CLI.  Leave 'expire after' blank if you dont want the token to expire.
• You will get authorization token.
• In CLI run  heroku login -i  and enter the authoriation token when it prompts for password.