Adding a sales receipt to Quickbooks Online with .NET using the IPP SDK API - api

Question

This probably has a really obvious answer, but I've been stuck searching for it for a few hours now.
I'm trying to figure out how to create the sales receipt using the sdk api, for linking a payment made by a customer to his invoice. As far as I can tell, if I don't do this, the payment will get deposited to the account but the invoice will never be updated.
I'm able to read invoices, make credit card or echeck payments, and read the customer record.
But I'm trying to create a sales receipt, and I'm not quite sure how to do it.
I can read the customer record but how do I add it to the sales receipt?
This just gives me a syntax error:
Customer customer = readCustomerUsingEmail(email);
SalesReceipt salesReceipt = new SalesReceipt();
salesReceipt.CustomerRef = Customer;
When I hover over customer, it states "Cannot implicitly convert type 'Intuit.Ipp.Data.Customer' to 'Intuit.Ipp.Data.ReferenceType'".
Edit: Ok. I'm now using the Payment object instead of the SalesReceipt object.
I think I've figured out the answer but I haven't run it yet. It just doesn't show a syntax error.
ReferenceType customerRef = new ReferenceType()
{
Value = customerData.Customer.Id,
name = customerData.Customer.DisplayName
};
payment.CustomerRef = customerRef;

Answer 1

You're attempting to do something very wrong here: create the sales receipt using the sdk api, for linking a payment made by a customer to his invoice
That is not what a sales receipt does.
Invoice - Indicates a customer owes you money.
Payment - Indicates a customer paid you money -- this is essentially the "other side" of an invoice. You create an invoice to indicate they owe money, and you create a payment to pay off the invoice.
Sales Receipt - Indicates a customer both owed you money and already paid. e.g. this is essentially an invoice and a payment combined into one object, for use when both the invoice and payment happened at the same time.
Soooo...
A sales receipt can not link to an invoice
A sales receipt is not used to link a payment to an invoice
What you should be doing is just creating a payment, and linking the payment directly to the invoice. To create a payment, you need to supply at minimum:
The customer (the CustomerRef field)
The total amount (the TotalAmt field)
A Line object (for use linking to an invoice)
The line Amount (if it's a payment for a single invoice this generally be equal to the TotalAmt field
A LinkedTxn node, which a link to the Invoice to pay (the TxnId field)
See the examples of creating a payment and additional docs here: https://developer.intuit.com/docs/api/accounting/payment
Example:
{
"CustomerRef":
{
"value": "20",
"name": "Red Rock Diner"
},
"TotalAmt": 55.00,
"Line": [
{
"Amount": 55.00,
"LinkedTxn": [
{
"TxnId": "69",
"TxnType": "Invoice"
}]
}]
}
There's tons of sample code here:
https://developer.intuit.com/docs/00_quickbooks_online/2_build/40_sdks/01_.net/0004_sample_code_and_sample_apps
And one specific to Payments here:
https://github.com/IntuitDeveloper/SampleApp-CRUD-.Net/blob/master/SampleApp_CRUD_.Net/SampleApp_CRUD_.Net/Entities/TransactionEntities/Payment.cs