If you clicked the MFA Setup link and were taken to a screen like below instead of being asked to it opened the site without asking you to login please take the following steps.
Go to the profile circle in upper right corner. click on this and choose ‘sign out’ Confirm on next screen to sign out the user.
Now that you have signed out you can click here to return to the MFA setup page and start over - you should now get the login box where can click to add an your Ameresco account.