Hi there, @YWWP.

Thank you for reaching out to the Community. I'd be glad to lend a hand with creating a refund check for a customer and posting it to a project.

At this time, a refund check option isn't available in QB Online, but there's an option to issue a Refund Receipt for a customer and post it to a project. You can use Refund Receipt to return funds for a service or item.

Here's how to record a refund receipt:

1. Sign in to your QuickBooks Online account.
2. Click on the New + icon.
3. Under the Customer section, select Refund Receipt.
4. Choose the drop-down in the customer option, locate the project, and under the project, click the customer.
5. Enter the additional refund information.
6. When you're ready, go to Save and Send. 

Here is also a screenshot as an example of choosing the customer to attach to the project: 

Please let me know if the information provided does the trick. If you have any more questions, I'm only a comment away. Have a safe and productive week ahead!