Thanks for keeping us updated about the steps that you've tried, @Lisa-S.
Allow me to step into this conversation and provide you with some details about recording customer refunds in QuickBooks Desktop.
You'll need to select the correct customer upon receiving payments so the Discounts And Credits option will be clickable.
However, if the issue persists after selecting a customer's name I'd suggest running the verify and rebuild process. Verifying the data self-identifies data issues within a company file while rebuilding the data resolves data integrity issues.
To do that:
Once done, you can proceed with verifying the data:
For detailed instructions on these steps, please refer to this article: Resolve data damage on your company file.
If the problem continues, I'd recommend getting in touch with our Customer Care Team. They have extra tools like screen-sharing that can help verify what's causing the issue.
That should do it.
Please let me know how it goes or if you have any other concerns with QuickBooks. I'll be around to help you out. Have a great day.