Hello there, @MBMaxwell.
Thanks for posting here in the Community. I'd be happy to help share some clarifications about the error that you received when creating deposits in QuickBooks Online.
If you've already added your current bank account to QuickBooks Online, make sure to change the account where the payments will be recorded. You can change this on your accounts and settings section.
Let me guide you how:
Once done, you can try creating a deposit again.
Here are some helpful articles that you can check out for more information about receiving payments in QuickBooks Online:
These resources should help you record your deposits successfully in QuickBooks Online.
Don't hesitate to reach back out to me if you need more assistance with applying deposits in QuickBooks. I'd be pleased to help. Have a great day!