You can create a vendor credit and add it under a certain project/customer, @heatingguys.

Doing so gives you the option to apply it to an open or future bill. Here's how to record it in QBO:

1. Click the + New button and choose Vendor credit.
2. Pick a vendor from the drop-down.
3. Depending on how the purchase is recorded, enter the Category details or Item details. Use the same category, product, or service you're getting credit for.
4. In the Customer/Project column, pick the right one from the drop-down.
5. Hit Save and close.

Once done, you'll find it under the Transactions tab of the customer/project selected on the vendor credit. Please see screenshot for visual reference:

When you're ready, you can apply it to a bill. Follow these steps:

1. From the project's Transaction tab, open the bill.
2. Click the Make payment button below the Balance Due amount.
3. In the Outstanding Transactions section, mark the bill.
4. Go to the Credits section and place a checkmark in the box next to the Vendor Credit.
5. Hit Save and close.

For more information about the process, take a look at this article: Enter a credit from a vendor. 

I want to know if you need anything else by leaving a comment. It's always a pleasure to help. Take care!