Implementing Receipt Validation in Swift 3

Question

I am developing an iOS app in Swift 3 and trying to implement receipt validation following this tutorial: http://savvyapps.com/blog/how-setup-test-auto-renewable-subscriptio

Answer 1

Eventually I was able to solve the problem by having my app call a Lambda function written in Python, as shown in this answer. I'm still not sure what was wrong with my Swift code or how to do this entirely in Swift 3, but the Lambda function got the desired result in any case.