QB Issue Resolution:

You can enter a comment in the description section of a separate line on the invoice without assigning any other detail (date/product/service/amount) to this line. You can also enter a comment in the ‘Message on invoice’ section.

Resolution for Issue 'How do i add a line on invoice for comment only, and not for product or service?' available: Yes (Solved).
Source: Intuit Community forum.

How do i add a line on invoice for comment only, and not for product or service?: 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 Description section
Quickbooks Repair Pro will resolve it efficiently and affordably. Guaranteed resolution of your issue, or you pay nothing!

Error Recovery for Description section [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: