I am unable to transfer money from Apple Pay to my bank account

try updating your bank account information:

How to update your bank account information

1. Go to your card info:

• • On iPhone: Open the Wallet app, tap your Apple Cash card, then tap the more button . 
  • On iPad: Open the Settings app, tap Wallet & Apple Pay, then tap your Apple Cash card.

1. Tap Bank Account, then tap the bank account you want to update. 

• • To delete your banking information, tap Delete Bank Account Information. Tap again to confirm. After deleting, you can add your bank information again or add different information. 
  • To edit your bank information, tap next to your routing number or account number, add your information, then confirm the numbers and tap Next.6

After you update your information on one device, it automatically updates on all the devices where you're signed in with your Apple ID.

Also make sure your bank is listed here - Apple Pay participating banks - Apple Support

What warning is it giving you?

try going to settings>general>reset>and reset your network settings.

try signing out of your Apple ID and back in.

Do you have a different bank account you can try or a different routing number?

when you called your bank did you call the local branch or the corporate office?

I am not sure either. I am out of ideas.