How do I account for invoice payment in the form of multiple checks covering a customer's remaining balance across multiple projects (checks dont match invoices)?

Thanks for the response. Let's say the balance on the invoice for Project A is $500, and the balance on Project B's invoice is $750. The customer sends me two checks, one for $300, and one for $950. Let's also say I have received and deposited these two checks on two different days. If I receive payment for the $950 check and apply it to Project B ($750 invoice), then the customer gets a credit of $200? And I can then subsequently receive payment for Project A and apply the $200 credit along with the $300 check?

EDIT: I tried this, and was successful, with some difficulty. In case someone else comes here looking for answers on this topic, it's important in the "Receive Payment" screen to use the parent customer and not the project name for the "Customer" field. If you try to apply payments with the project as the customer, QBO will not allow you to access the parent customer's credits to be used as payment. With the parent customer in the "Customer" field, I have access to all of the invoices from various projects, and any payment that exceeds the invoice in question will result in a credit on the customer's account, which can be applied to another project's invoice, but again, only if you use the parent customer as the "Customer". Thanks for the insight, everyone.