I’m here to share some information about QBO’s packing slip, @DianaA.

You can send an invoice or sales receipt to your customers with a paid watermark on it. However, the feature to customize or set the packing slip as paid in QuickBooks Online (QBO) is currently unavailable. But that's a great feature if it will be added to the current features that we have. I'll be sure to take note of it. For now, you can visit the QuickBooks Blog to check for new updates and features that we have. 

Here's how to send a paid invoice or sales receipt:

1. From the left menu, click Sales and choose the Invoices tab.
2. Find the invoice or the sales receipt that was marked as paid.
3. Under the Actions column, click the drop-down and select Send.
4. Enter the email address under the TO section.
5. Click Send.

You can read this article for your reference: How to Email or Print an Invoice.

For more information about packing slips, check out this article: Create and print a packing slip.

You can always leave a reply below if you have any other questions with your packing slips and or anything else. I'll be here if you need further assistance. Take care and have a wonderful day!