SwiftyStoreKit.verifyReceipt method is not working

## Bug Report
Hello I am using SwiftyStoreKit.verifyReceipt method for verify receipt validation but its always return failure like user has not purchased this plan I am checking it after purchase product

I am using below code

let appleValidator = AppleReceiptValidator(service: .sandbox, sharedSecret: "xxxxxxxxxxx")

SwiftyStoreKit.verifyReceipt(using: appleValidator) { result in
switch result {
case .success(let receipt):
print(receipt)
let productId = "user_subscription_purchase_id"
// Verify the purchase of a Subscription
let purchaseResult = SwiftyStoreKit.verifySubscription(
ofType: .autoRenewable, // or .nonRenewing (see below)
productId: productId,
inReceipt: receipt)

switch purchaseResult {
case .purchased(let expiryDate, let items):
print("\(productId) is valid until \(expiryDate)\n\(items)\n")
case .expired(let expiryDate, let items):
print("\(productId) is expired since \(expiryDate)\n\(items)\n")
case .notPurchased:
print("The user has never purchased \(productId)")
}

case .error(let error):
print("Receipt verification failed: \(error)")
}
}

## Platform Information
- OS: [e.g. iOS 13.4]
- Purchase Type: [auto-renewable subscription]
- Environment: [sandbox]