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.
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. Your GitHub Student Credit will not be issued until you verify your credit card with Heroku.
More information can be found in the Dev Center about 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:
If you have had a credit card on file for more than a week and still did not receive your credits, please send an inquiry to firstname.lastname@example.org.
Paying for Heroku Services
The credit card on file is only charged if paid provisions are utilized beyond the monthly allotment of GitHub credits.
To learn more about the GitHub Student Developer Pack, please view our current program description: https://www.heroku.com/github-students