How to create SOAP on Apply (update) payment.

Hi team.

Example:

We have a payment PAY123 - 500$

Invoice INV123 - 500$,

We applied 100$ from this payment (PAY123) to the invoice (INV123).

After a few days, we want to apply the rest 400$ from payment PAY123 to invoice INV123.

If we are applying that 400$ to the invoice using the "update" SOAP function, it doesn't sum the previous payment 100$ and the additional 400$ that we want to apply, this function is deleting the old record (100$) and creates a new one (400$). So the "Amount Due" of the invoice became 100$.

How we can do this via SOAP request in the right way?

The expected result is a fully applied payment to the invoice.