After I capture "snap" a picture of a receipt I can see it on the app and QB online and can create a new expense but how do I attach the receipt(s) to an invoice.

Welcome to the Community, jennifer87.

I appreciate your interest in learning more about the receipt feature in QuickBooks Online (QBO).

There are two ways to add your uploaded receipts to invoices, however, there isn't an option to do this on your mobile app. 

The first option is to go to your Receipts tab and from there you can select the receipt and create the expense.

Here's how:

1. Log into your account using a browser.
2. Go to Banking.
3. Choose the Receipts tab.
4. Under For review, select the uploaded receipt.
5. Click Create expense.
   

Another way, to add receipts to your invoice is to use it as an attachment. I'd be happy to walk you through the steps on how to do it:

1. Go to the +New icon.
2. Click Invoice.
3. Fill in the necessary information.
4. From the Attachments section, click the Show existing link.
5. A side tab will pop up where you can choose the receipt you want to attach. Click Add.
   
6. Hit Save and close.

I've got an article made available so you'll become more familiar with managing receipts in QuickBooks: Capture and categorize receipts in the Receipts tab.

Just so you want to know more about emailing your receipts into QBO, you'll want to keep this article handy: Email receipts and bills to QuickBooks Online.

I'll be right here if you need anything about QuickBooks. Wish you all the best.

thank you.