Thank you for getting back to us here in the Community, OlAl.

Turning off the automatic credits function helps apply credits to specific invoices in QuickBooks Online (QBO).

If you'll want to turn it off, it won't affect the credit in your future invoices.

For future reference, you can check out this article to learn how to manage overpayment: Customer credit or overpayment in QuickBooks Online

Stay in touch if you have any other questions aside from this. Have a great day!