App store receipt request always fails

I am performing this:
```
let appleValidator = AppleReceiptValidator(service: .production, sharedSecret: "xxxxxxxxxxxx")
SwiftyStoreKit.verifyReceipt(using: appleValidator, forceRefresh: true) { result in
switch result {
case .success(let receipt):
print("success: \(receipt)")
case .error(let error):
print("Verify receipt failed: \(error)")
}
}
```

Getting the **sharedSecret** key from the AppStore Connect portal under my app -> in app purchase -> secret key

I tried to use ._production_ and ._sandbox_ **service** but I always go into failure "case .error" with this message:
`Verify receipt failed: networkError(error: Error Domain=SKErrorDomain Code=0 "An unknown error occurred" UserInfo={NSLocalizedDescription=An unknown error occurred, NSUnderlyingError=0x28182ba20 {Error Domain=ASDServerErrorDomain Code=500317 "Unhandled exception" UserInfo={NSLocalizedDescription=Unhandled exception, NSLocalizedFailureReason=An unknown error occurred}}})`

Any solution?