QB Issue Resolution:

A c/memo is only used to credit the customer in AR, which is not what you did. You gave them money, so it’s a Refund Receipt, which reduces your bank balance. The original invoice is not involved in the new transaction

Resolution for Issue 'I have a customer that fully paid their invoice up front for two student enrollments in our program (so, two line items on the invoice). She now needs to un-enroll one of the students. We’ve given her the refund, but it’s unclear how to record this in QBO. We tried creating a Credit Memo, but it won’t let us apply it to the invoice in question, since the invoice has already been paid.' available: Yes (Solved).
Source: Intuit Community forum.

I have a customer that fully paid their invoice up front for two student enrollments in our program (so, two line items on the invoice). She now needs to un-enroll one of the students. We’ve given her the refund, but it’s unclear how to record this in QBO. We tried creating a Credit Memo, but it won’t let us apply it to the invoice in question, since the invoice has already been paid.: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

Support for Invoice
Quickbooks Repair Pro will resolve it efficiently and affordably. Guaranteed resolution of your issue, or you pay nothing!

Error Recovery for Invoice [Canada]
E-Tech is the #1 Quickbooks data migration and Conversion service provider.

Get 50% off Quickbooks Online

Click Here for 50% off!

Additional Support Options: