API for sales comment lines

I have copied page 30044 “APIV2 - Sales Order Lines” and I am using that successfully. I have even added a few additional fields (like Item References and setting/reading this successfully).

I now need to add Sales Comment Lines to these like this:


The problem with the above is you dont have direct access to the Sales Order Document No. field from the “Sales Invoice Line Aggregate” table on which this API is built.

Has anyone done this or can anyone help to get this link established?
TIA
Heinrich