How you dispute a payment made with Apple Pay depends upon the means of transaction.
For payments made with Apple Pay Cash with Messages, see the section about "How to cancel or dispute a payment" [made with Apple Pay Cash]" by clicking on the link for this document: Send, receive, and request money with Apple Pay - https://support.apple.com/HT207875
"How to cancel or dispute a payment [made with Apple Pay Cash]
1. Open the Messages app, then open the conversation and tap the payment.
2. Your Apple Cash card will open in the Wallet app. Under Latest Transactions, tap the payment, then tap it again.
3. Tap Cancel Payment."
Notes:
- If you don't see Cancel Payment, the person has already accepted the payment. Try asking the recipient to send the money back to you instead.
- It can take 1-3 business days for the money to be refunded, depending on your bank or card issuer.
- Apple Pay person to person payments are just like any other private transaction between two people. If you're unable to cancel or receive your money back from the recipient, you can contact [Apple] to open a dispute [ https://getsupport.apple.com/?caller=kbase&PGF=PGF90000&category_id=SC0287&symptom_id=23288 ].
For payments made with Apple Pay see the section about "Report a transaction with the wrong merchant name or location" by clicking on the link for this document: How to use Apple Pay - https://support.apple.com/HT201239#history
"Report a transaction with the wrong merchant name or location
1. On your iPhone, open the Wallet app and tap the card that you made the transaction with.
2. Under Latest Transactions, tap the transaction that you want to report.
3. Tap Report an Issue.
4. Under Issue, tap Incorrect Merchant Info, then tap Merchant Name, Merchant Category, or Other Issue."