Can the Payment Instructions box on an invoice be edited?

I can guide you in editing the invoice payment instructions, @ cforsythelectric. 

If you referring to the message on invoice in QuickBooks Online, we can customize it through View/Edit under Action or Modify it from Sales Form.

Here's how to customize it from View/Edit. 

1. On the left pane click the Sales menu then choose Invoices. 
2. Select the specific invoice you want to be edited.
3. Drop-down arrow under Actions select View/Edit. 
4. On the Message on invoice you can modify it. 
5. Click Save and send.  

Here's how to modify it through Sales Form: 

1. Click the Gear Icon and choose Custom Form Styles. 
2. Under New style drop-down arrow and select Invoice. 
3. Tap the Content then click the pencil icon from the lower right corner. 
4. Enter the message you want to modify. 
5. Click Done once finish.

You can refer to these articles on how to modify your invoices, estimates, and sales receipts in QuickBooks Online:  

• How to Customize Invoices in QuickBooks Online 

• Customize invoices, estimates, and sales receipts in QuickBooks Online 

We're always available here and ready to help if you need assistance in completing your task with QuickBooks. Stay safe and healthy.