ReceivePayment

In a ReceivePayment message, each AppliedToTxnRet aggregate represents the transaction to which this part of the payment is being applied. Four types of transactions can receive payments in QuickBooks: invoices, statement charges (though not through the SDK), general journal debits, and checks. (For example, a customer’s job might receive a payment reimbursing a check that was written for an expense for that customer’s job.)

Or use:

IsAutoApply
If IsAutoApply is true, QuickBooks applies TotalAmount to any outstanding transaction that exactly matches TotalAmount. If no exact match is found, the payment is applied to the customer job’s outstanding transactions, beginning with the oldest one.

How to use IsAutoApply in LetSync Desktop. You will have to set the EditSequence = applyall on the record that you want to use it

FIELD NAME	FIELD NAME (old)	QUERYABLE	UPDATEABLE	REQUIRED ON UPDATE	INSERTABLE	REQUIRED ON INSERT
TxnID		true	false	true	false	false
TimeCreated		true	false	true	false	false
TimeModified		true	false	true	false	false
EditSequence		true	false	true	false	false
TxnNumber		true	false	false	false	false
CustomerRef_ListID		true	true	optional	true	true
CustomerRef_FullName		true	true	optional	true	true
ARAccountRef_ListID		true	true	optional	true	optional
ARAccountRef_FullName		true	true	optional	true	optional
TxnDate		true	true	optional	true	optional
RefNumber		true	true	optional	true	optional
TotalAmount		true	true	optional	true	optional
CurrencyRef_ListID		true	false	false	false	false
CurrencyRef_FullName		true	false	false	false	false
ExchangeRate		true	true	optional	true	optional
TotalAmountInHomeCurrency		true	false	false	false	false
PaymentMethodRef_ListID		true	true	optional	true	optional
PaymentMethodRef_FullName		true	true	optional	true	optional
Memo		true	true	optional	true	optional
DepositToAccountRef_ListID		true	true	optional	true	optional
DepositToAccountRef_FullName		true	true	optional	true	optional
UnusedPayment		true	false	false	false	false
CCTII_CreditCardNumber	new	true	true	optional	true	optional
CCTII_ExpirationMonth	new	true	true	optional	true	optional
CCTII_ExpirationYear	new	true	true	optional	true	optional
CCTII_NameOnCard	new	true	true	optional	true	optional
CCTII_CreditCardAddress	new	true	true	optional	true	optional
CCTII_CreditCardPostalCode	new	true	true	optional	true	optional
CCTII_CommercialCardCode	new	true	true	optional	true	optional
CCTII_TransactionMode	new	true	true	optional	true	optional
CCTII_CreditCardTxnType	new	true	true	optional	true	optional
CCTRI_ResultCode	new	true	true	optional	true	optional
CCTRI_ResultMessage	new	true	true	optional	true	optional
CCTRI_CreditCardTransID	new	true	true	optional	true	optional
CCTRI_MerchantAccountNumber	new	true	true	optional	true	optional
CCTRI_AuthorizationCode	new	true	true	optional	true	optional
CCTRI_AVSStreet	new	true	true	optional	true	optional
CCTRI_AVSZip	new	true	true	optional	true	optional
CCTRI_CardSecurityCodeMatch	new	true	true	optional	true	optional
CCTRI_ReconBatchID	new	true	true	optional	true	optional
CCTRI_PaymentGroupingCode	new	true	true	optional	true	optional
CCTRI_PaymentStatus	new	true	true	optional	true	optional
CCTRI_TxnAuthorizationTime	new	true	true	optional	true	optional
CCTRI_TxnAuthorizationStamp	new	true	true	optional	true	optional
CCTRI_ClientTransID	new	true	true	optional	true	optional
CustomField1		true	true	optional	true	optional
CustomField2		true	true	optional	true	optional
CustomField3		true	true	optional	true	optional
CustomField4		true	true	optional	true	optional
CustomField5		true	true	optional	true	optional
CustomField6		true	true	optional	true	optional
CustomField7		true	true	optional	true	optional
CustomField8		true	true	optional	true	optional
CustomField9		true	true	optional	true	optional
CustomField10		true	true	optional	true	optional
CustomField11		true	true	optional	true	optional
CustomField12		true	true	optional	true	optional
CustomField13		true	true	optional	true	optional
CustomField14		true	true	optional	true	optional
CustomField15		true	true	optional	true	optional
ExternalGUID		true	true	optional	true	optional
UserData	user field
Operation	add,update,delete

AppliedToTxnRet

CCTII ->CreditCardTxnInputInfo
CCTRI ->CreditCardTxnResultInfo

Adding new record: EditSequence=’ApplyAll’

If ApplyAll is set, QuickBooks applies TotalAmount to any outstanding transaction that exactly matches the total amount. If no exact match is found, the payment is applied to the customer job’s outstanding transactions, beginning with the oldest one.
If IsAutoApply isn’t set, QuickBooks receives the payment but does not apply it to any outstanding transaction. Instead, the amount will appear as a credit on the customer job’s next transaction.
Or you can set:

AppliedToTxnRet.PARENT_IDKEY -> ReceivePayment.TxnID
AppliedToTxnRet.TxnID -> Invoice.TxnID