The Quickstart is in Node and if it helps we do have an example in C#. Currently all our examples have the amount hard coded in the payment request. This is cause the Web Payments SDK is used for tokenizing the card and it’s entirely up to you and what best fits your business need to pass the amount to the CreatePayment request.
As for the change you had to make what are the steps to reproduce? We’ve been unable to replicate the error. 