How do I add an Excel spreadsheet to an invoice?

Welcome to the Community space, @bnceramics. I can surely guide you through the process of adding an Excel spreadsheet to your invoice in QuickBooks Online (QBO). 

Yes, we can add an Excel spreadsheet to your invoice. However, we need to make sure that the file is in XLSX format and has a maximum file of 20MB only. 

Here's how: 

1. Go to the + New icon, and select Invoice. 
2. Scroll to the bottom part of the page. 
3. Click Attachments and choose the file under XLSX format. 
4. Once it loads up, tick the Attach to email box.
5. Once done, select Save. 

The screenshot is attached for visual reference for the old and new layouts. 

Additionally, I've added this article for you to check if you want to personalize your sales forms in QBO: Customize invoices, estimates, and sales receipts in QuickBooks Online.

Feel free to reply to this thread if you need additional assistance in adding attachments to your sales form and any QBO-related queries. Keep safe.