tax code on journal posting via IDOC

Hi Experts,

I have scenario where I need to remove the tax code being entered in journal posting via Idoc.

I have recreated scenario in test system with only 1 segment in the idoc (type WPUUMS01) with material number and value.

When the idoc is processed I can see the posting doc and there is a line for my value but with a GL and tax code assigned. (line2)

I cannot find the link between GL and material number even checked valuation class and assignments.

I want to find where the tax code & GL is being 'pulled' from when the idoc is processed.

Aim is to post the idoc without it posting a tax code as the GL is set to posting without tax allowed.

Thanks