If you want to set the permissions for sales people so that they can view an invoice but not be able to create, edit or delete and invoice, that setting should not then cause them to lose the ability to request or process a payment.

I want salespeople to be able to request a 30% deposit from an estimate. This in no way relates to an invoice.

I want them to be able to process a deposit or a final payment for a job while they are at the house. They should be able to do this.

If users want to set limits on employees ability to request or process payments then it should have it's own settings just like "credit memos" is separate from "invoices" in the role access settings.