You have a Personal Heroku account and have applied to the GitHub credits program. You're curious if you need to have a credit card on file to receive credits.
The Heroku GitHub Student Offer is no longer accepting new applications. If you have already received credits, you will not be affected by this change. Current participants can continue to use the remainder of their credits for the allotted time. For information on free Heroku resources for students, please visit here.
Credit card verification is a security requirement for all Heroku accounts wishing to use custom domains, third-party add-ons, and to purchase Hobby Dyno or higher plans.
More information can be found in the Dev Center about Heroku Account Verification:
Adding a card to Your Personal Heroku account
You can add a card to your Personal Heroku account by going to the Billing tab under Account Settings:
Paying for Heroku services
The credit card on file is only charged if paid provisions are utilized beyond the monthly allotment of GitHub credits.