How do I send money back if I haven’t set up my apple pay

okay, now we are at a point where I can post this -

To set up Apple Cash Family you must first close any accounts that children already had. Make sure that the balance is zero then go here - Manage your Apple Cash account - Apple Support next, go here - Set up and use Apple Cash Family. (Additional support links View and limit your child or teen's Apple Cash activity, Leave Apple Cash Family, Apple Cash and person to person payments limits)

Ah, it wont expire if you accepted it. It sounds like you had Apple Cash set up but once you accepting it your Apple Cash became restricted or locked.

If your Apple Cash is locked or restricted you must go here to start the lengthy process of getting it unlocked or the short process to get it unrestricted - If your Apple Cash account is restricted or locked - Apple Support

Go to your Apple Cash card

• iPhone: Open the Wallet app, then tap your Apple Cash card.
• iPad: Open the Settings app, tap Wallet & Apple Pay, then tap your Apple Cash card.
• Apple Watch: Open the Apple Watch app on your iPhone, tap Wallet & Apple Pay, then tap your Apple Cash card.

You'll see the option to Verify Identity or Contact Apple Support. Tap one, then follow the onscreen steps. Learn more about identity verification. 

1. Where are you located?
2. Are you at least 18?

if you did not set up Apple Cash, you don't need to send the money back. It will expire and return to the sender.

about a week and then a week after that it should return.

show my a screenshot of where it says it was accepted. please edit out personal information.

Nowhere in those screen shots does it say you accepted the money transfer.

You can not set up ApplePay Cash for yourself if you are under 18.