Hi Mustapha,
I do apologise for the confusion! In fact, you must first toggle on our Withholding Tax feature by heading to Settings > Configure System > Toggle Features > Accounting > Tick Withholding Tax. Once this is done, you can then create a Withholding Tax account code with the relevant percentage; please ensure that the Show in Sales box is ticked and saved.
After this, you can then create the invoice for 10,000 coded to the Withholding Tax account. The system would then calculate the Withholding Tax amount based on the rate you've entered when creating the account code. Lastly, when you receive the tax back, you should create an invoice for this amount and code it to Withholding tax account.
I hope this helps!
Tommy