QB Issue Resolution:

You can do both.

Personally I would send the full invoice.  Because if you pre-enter the expected witholding amount theres a chance the customer will still only send you 85% – leaving you short.

So send the full invoice, receive a cash payment against the invoice, then adjust the invoice by adding witholding to zero out the balance due.

Resolution for Issue 'How do I invoice a client from a country which requires payment amount to be net of income tax?' available: Yes (Solved).
Source: Intuit Community forum.

How do I invoice a client from a country which requires payment amount to be net of income tax?: 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 balance due
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Error Recovery for balance due [Canada]
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