Allow me to chime in on this thread to help you with applying the invoice custom template in QuickBooks Online (QBO), joanfye.

When applying the custom template to your invoice, you’ll want to double-check if you’re using the correct template you preferred. To check, you can follow the steps below:

1. Navigate to the Sales menu and select the Invoices tab.
2. From there, locate the specific invoice you want the template to be applied to.
   
3. In the transaction window, tap the Customize section at the bottom and select your preferred template.
   

If you want this to be automatically applied to future invoices. You can set this up as your default to prevent you from changing the template all the time. Here’s an article you can check out to do the following and refer to Step 7: Set a default custom template: Customize invoices, estimates, and sales receipts in QuickBooks Online.

For future assistance, you can visit this resource to get equipped with recording invoice payments once your clients decide to pay.

Should you have more concerns with custom templates, please let me know by adding a comment below. I’m always here to help. Have a good one!