How do you add a second bank account for money transfers to the Apple wallet?

If you want to do instant transfers, you need to a debit card issued by a bank that support Apple Pay. Occasionally the bank that issued the debit card will charge a fee. Some banks do not charge fees for instant transfers. All banks will do a free ACH transfer. ACH transfers take 1 to 3 days, but exclude weekends and holidays. So, a transfer started today via ACH, may not reach your bank until maybe Thursday or Friday at the latest.

Please follow the step by step instructions to add additional debit cards/banks to your Apple Wallet.

Transfer money in Apple Cash to your bank account or debit card - Apple Support

What is Apple transfer? What are you trying to do, add a debit card, add account numbers (routing and account)? Where is the money coming from and where do you want it to go, Apple Card MasterCard, Apple Cash, Apple Savings?