Not able to update tax eConnect GP 2016

LNITMSEQ is the Line item sequence and defaults to 0. The documentation states "Header level taxes only specify tax information when the line sequence element of the <taSopLineIvcTaxInsert> XML node is set to 0", so you must be calculating the tax in each line item, rather than on the subtotal as a whole?

Setting the LNITMSEQ value would work in that scenario, not in the scenario where the tax information is specified only in the header, I believe.

guys did you try pu this field

linetax.LNITMSEQ 

that works to me 

taSopLineIvcTaxInsert_ItemsTaSopLineIvcTaxInsert linetax = new taSopLineIvcTaxInsert_ItemsTaSopLineIvcTaxInsert();
linetax.CUSTNMBR = ClientOriginalId(order.Client);
linetax.LNITMSEQ = detail.Id; 
linetax.SOPTYPE = SOPTYPE;
linetax.SOPNUMBE = salesHdr.SOPNUMBE;
linetax.SALESAMT = line.XTNDPRCE;
linetax.TAXDTLID = tProdcodeid1.Value;
linetax.STAXAMNT = line.TAXAMNT;
linestax.Add(linetax);

so in few words we can't use tax per line?

This issue has not yet been solved, unfortunately.

According to the eConnect Programmers Guide, tax values can be set/updated at the header level by settings values on the <taSopHderIvcInsert> XML node along with the <taSopLineIvcTaxInsert> XML node.

As far as I can tell, and what the documentation states, we should be including all the correct data, but if we pass in a taSopLineIvcTaxInsert_ItemsTaSopLineIvcTaxInsert object (which gets serialized to the <taSopLineIvcTaxInsert> node), eConnect throws the exception OP outlined. If we don't include this information, we get a valid response, but the tax is not updated.

i have the same problem did you solved this issue?