QB Issue Resolution:

there is no item type in QBO that will do any kind of % calculation, you have to calculate the amount and enter it

Resolution for Issue 'Can i add a sub-charge to an invoice?' available: Yes (Solved).
Source: Intuit Community forum.

Can i add a sub-charge to an invoice?: 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 Invoice
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Error Recovery for Invoice [Canada]
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