I have a workaround on this, @grantlisa-brydon. 

It only takes a few clicks to create an invoice template in QuickBooks Online. Add I'm happy to outline the detailed steps with you so you'll be a pro in no time.

Good news because QuickBooks Online (Simple Start, Essential, Plus, and Advance) has a feature that you can customise the appearance and layout of your sales forms (Invoice, Quote, and Sales receipt). To do this, follow the steps below: 

1. Go to the Gear icon and choose Customer form styles. 
2. Select New style and pick Invoice. 
3. In the Design section, you can add a template, logo, color, font, and EFT information. 
4. Select the Content button. 
5. Click the three pencil icon one at a time and input the details you want to add. 
6. On the Email page, you can update the Standard and Reminder email for that specific customer. 
7. Click Done. 
8. Hit the drop-down arrow beside Edit and rename the template name. 

For more details, see this link: Customise invoices, quotes, and sales receipts in QuickBooks.

Every time you create an invoice for this specific client, ensure to use the personalized template you created. Here's how to check if you use the correct template: 

1. In the Invoice form, click the Customize button in the bottom part. 
2. Select the template you've created. 
3. You can also hit the Print or Preview to see what the forms look like. 

Additionally, ensure that you have a default invoice template for other customers. As a result, the custom template you created will not apply to another customer.

Did you know that you can create recurring invoices so you can use the same template? To learn more about this functionality, please click this link: Create recurring transactions in QuickBooks.

Further, check out these articles below on how to customise your invoice template using a mobile application and manage your customer payments: 

• Receive payments for invoices
• Customise invoices on the QuickBooks Online mobile app

Do you have questions about other processes? Add them to your reply, and I'll assist you. Keep safe always, grantlisa-brydon.