Is it possible to attach receipts to an invoice?

Yes, it is, tristanwebber0-i.

You can upload images from your computer and attach receipts to an expense transaction. 

For now, you can utilize the Add logo or link on the Notes to Customer field. 

We'll take this as a product suggestion. We'll take this as a product suggestion. With your feedback, our engineers might add this future product enhancement. You can also check out our QuickBooks Blog to stay updated with the latest features of our product.

Also, here's an article you can read about recording and attaching expense receipts for additional information: Record or attach expense receipts in QuickBooks Self-Employed.

Tag me if you need anything else, @tristanwebber0-i. I'll be right here to help.