Hi,
verifyReceipt is deprecated. You should use jwsRepresentation of success purchase result
switch try await product.purchase() {
case .success(let result):
let jws = result.jwsRepresentation
// send jws to your backend
And check it on your backend.
For more details try to google article "How to Validate iOS and macOS In-App Purchases Using StoreKit 2 and Server-Side Swift". It's very useful.