By default, custom payments will be turned on. This allows your clients to create and send you custom payments in your payment portal, that are not linked to a payment request. To turn this feature off (or back on), follow the steps below.
Step-by-step instructions:
First, click your logo icon in the top left corner and select "Settings".
Select "Payment Portal".
Locate the "Allow custom payments" row under "payments" and change the corresponding toggle from "On" to "Off".
When this is turned off, your customers can only pay payment request you sent them. They cannot send you a payment for a custom amount.