QB Issue Resolution:

create a service item called something like holiday charge, select an income acct on the item screen, use that on the invoice

Resolution for Issue 'How do i add an extra fee (ex. charge for holidays) to my invoice? I am using QB online' available: Yes (Solved).
Source: Intuit Community forum.

How do i add an extra fee (ex. charge for holidays) to my invoice? I am using QB online: 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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