It's not uncommon for customers to get confused during the "Make Payment" flow: they'll check the checkbox to pay an invoice, also enter the amount due into the "Other Payment Amount" box, and then make a payment for twice the amount they intended.

We don't really have a need for customers to pay arbitrary / non-invoiced amounts, so we'd rather just hide the "Other Payment Amount" UI element. It would be nice to have an option to do this.