Questions about the return value and processing order of the VerifyPurchase function

[pekochun]

I tried a function like this:

    func verifyPurchase(productId:String,sharedSecret:String) ->String {
        var returnValue = "none"
        let appleValidator = AppleReceiptValidator(service: .production, sharedSecret: sharedSecret)
        SwiftyStoreKit.verifyReceipt(using: appleValidator) { result in
            switch result {
            case .success(let receipt):
                let purchaseResult = SwiftyStoreKit.verifyPurchase(productId: productId, inReceipt: receipt)
                switch purchaseResult {
                case .purchased:
                    print(productId+"_purchased")
                    returnValue = "purchased"
                    
                case .notPurchased:
                    print(productId+"_notPurchased")
                    returnValue = "notPurchased"
                }
            case .error:
                print(productId+"_error")
                returnValue = "error"
            }
        }
        return returnValue
    }

　print(verifyPurchase(productId:xxxxx,sharedSecret:xxxxx) )

However, the function always returns "none" even if the purchase is successful. What is the order in which the VerifyPurchase function is processed? How can this function return the correct value?