What are the acceptable forms of payment towards a Apple Credit Card Bill?

A bank account or Apple Cash. See the "Choose or change a payment source" section of How to make Apple Card payments - Apple Support

Hello!

You should be able to pay your account balance using any bank account that you have linked to the card. You can find various how to videos at the link below including one on how to make payments.

Apple Card How-To Videos: https://www.apple.com/apple-card/how-to-videos/

Let me know if this helps!

ACH transfer from a bank.