Supporter Options During Signup

Could you please provide further information on how the Supporter plugin integrates with the signup form?

In the Support settings, I have clicked, “Puts a supporter signup option on the signup page.” However, I do not see a supporter signup on the signup page (when using wp-signup.php or wp-signup.php?Plus=1)

Please advise.

My goal is I would like to give a user the option in the signup form to either proceed with the limited demo or pay for the Supporter extras for x months as per the Supporter settings..