Does QBO ever automatically applies open credits to open customer invoices? If yes, how do I stop it?

Hi there Tim. I appreciate you for reaching out to us here in the Community. I'll share with you some information about open credits in QuickBooks Online (QBO).

Yes, the system will automatically apply the available credits to the overdue customer invoices once the feature is enabled through the Account and Settings window. You can turn it off following these steps:

1. Sign in to your QBO account.
2. Go to the Gear icon, then click on Account and settings.
3. Tap on Advanced at the left pane, then go to the Automation section.
4. Select the pencil icon, then disable the Automatically apply credits option.
5. Hit Save, then Done.

From there, the credit will no longer be applied to your invoices automatically. You can get more tips about handling customer credits through this article: Handle a customer credit or overpayment in QuickBooks Online.

When you're ready to record an invoice payment, you can check out this article as your reference: Record invoice payments in QuickBooks Online.

Please let me know if you have any other questions about customer credits. I'm always here to help. Keep safe!