QB Issue Resolution:

Click the gear in the upper right of your Home screen.
Choose Company Settings from the dropdown.
Click Form Delivery on the left side of your screen.
Click Customize to be brought to where you can edit your sales form templates.

Resolution for Issue 'How do I edit my QuickBooks Online Invoice Template?' available: Yes (Solved).
Source: Intuit Community forum.

How do I edit my QuickBooks Online Invoice Template?: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

Support for Customize templates
Quickbooks Repair Pro will resolve it efficiently and affordably. Guaranteed resolution of your issue, or you pay nothing!

Error Recovery for Customize templates [Canada]
E-Tech is the #1 Quickbooks data migration and Conversion service provider.

Get 50% off Quickbooks Online

Click Here for 50% off!

Additional Support Options: