How apply order amount in pre payment calculation

Hi ​@vannakheng 

Apply to Order reserves payment only up to the not-invoiced portion of the sales order. Any excess payment remains as an Available Balance until future invoices are created.

Payment Amount = 2,055.50
Transferred to Invoice = 1,939.50
Write-Off Amount = 32.00

(2,055.50 − 1,939.50) − 32.00 = 84.00

The remaining usable payment is 84.00.

Acumatica then compares the remaining payment with the not-invoiced sales order amount and applies only the lesser of the two.

In this case, the remaining payment (84.00) is greater than the not-invoiced order amount (34.00), so 34.00 is applied to the order, and the balance remains available.

Hope this helps