I need to know the merchant for Apple Pay transaction

If it was your Apple Card open the Wallet, tap on the Apple Card image and it will list all of the transactions with the merchant’s name. If it was any other card log in to the issuer’s website and it will list all transactions with the merchant’s name.

If your transaction says “Apple.com/bill” then Apple was the merchant. You can go to Settings/[your name]/Media & Purchases/View Account (log in)/Purchase History and it will list all of the charges from Apple.

Apple Pay is a service that allows credit and debit cards to be used for contactless transactions. Your iPhone is just a passthrough for those transactions. So you would check the online site or app for the issuer of the card that you used. If that isn’t what you mean please explain.

It still isn’t clear what your question is. Does this answer it→If you see 'apple.com/bill' on your billing statement - Apple Support