PayPal Rest API - Execute Payment with updated transaction info

I'm using C# and PayPal Rest API to Get an approved payment and execute it. But, I need to update the transactions associated with approved payment. The PayPal documentation reads:

Use this call to execute (complete) a PayPal payment that has beenapproved by the payer. You can optionally update transactioninformation when executing the payment by passing in one or moretransactions.

Here's my code

//Update the payment details in case totals changed because of a new address/zipcodeDetails amountDetails = new Details();amountDetails.subtotal = ValidationHelper.GetString(prices[Order.CartPricesEnum.Subtotal], "0");amountDetails.tax = ValidationHelper.GetString(prices[Order.CartPricesEnum.Tax], "0");amountDetails.shipping = ValidationHelper.GetString(prices[Order.CartPricesEnum.Shipping], "0");Amount amount = new Amount();amount.total = ValidationHelper.GetString(prices[Order.CartPricesEnum.Total], "0");amount.currency = "USD";amount.details = amountDetails;//update the transaction to make sure we have accounted for any updated pricesTransactions trn = new Transactions();trn.amount = amount;List<Transactions> trns = new List<Transactions>();                    trns.Add(trn);//Create a payment execution objectPaymentExecution paymentExecution = new PaymentExecution();paymentExecution.payer_id = payPalPayerID;paymentExecution.transactions = trns;                    //Execute (complete) the paymentPayment newPayment = payment.Execute(accessToken, paymentExecution);

The problem is that when when this runs I get the following error:

{"name":"VALIDATION_ERROR","details":[{"field":"transactions[0].total","issue":"Required field missing"},{"field":"transactions[0].currency","issue":"Required field missing"},{"field":"transactions[0].amount","issue":"This field name is not defined for this resource type"}],"message":"Invalid request - see details","information_link":"https://developer.paypal.com/webapps/developer/docs/api/#VALIDATION_ERROR","debug_id":"bcba38f3c56d7"}

This is telling me that I'm missing .total and .currency, and that the .amount field is not defined. However, you can plainly see that I am setting the total and currency, and the amount field is the ONLY field that you can set on the transactions object according to the PayPal API documentation:

transactions
array of transaction objects
Transactional details if updating a payment. Note that this instance of the transactions object accepts only the amount object.

So, my question is: How can I take an approved payment, update the price on the transaction of the payment and then execute that payment?