Do I need to pay withholding tax for digital advertising fee?If I did not make payment for withholding tax, is the advertising fee tax deductible?

If you are paying the digital advertising fee to a non-resident for the usage of an application, then the digital advertising fee is subject to withholding tax because it is deemed as a royalty payment.
If the withholding tax is not remitted to the Inland Revenue Board, then the digital advertising fee will become not tax deductible.