Hi,
I am have a similar problem. While investigating and seeing the suggestions made in this post, I tried to pass the TAX condition in E1WPB03 instead of E1WPB04. (i did this by manually editing an existing IDOC).
By doing this I was able to pass the TAX Amount and the pricing procedure in the POS Inbound in SAP ERP was able to accept it. The only challenge here is that once you use the E1WPB03, the ERP system treats TAX as a normal condition like tender or discount and it does not execute the tax code determination in ERP.
@Issam : Could you share the code you used ?
Isn't there a BADI ?
Regards,
Dheeraj