A/R Payment – Live Calculation for Payment & Unapplied Amount + Submit Button

Requesting:

1. Make Payment Amount adjustable (live) rather than fixed, with Unapplied Amount updating in real time as invoice payments are entered (similar to A/P).

2. A separate Submit button, distinct from Save, so we can review before posting.

Reason:
Because the Unapplied Amount doesn't calculate live and tax decimal rounding hides the exact difference, we can't confirm the correct payment amount until clicking Save — which both posts the transaction and blocks any correction other than "Reverse," which itself impacts the GL.