In Ostendo there are tax matrix's that are linked to an items product tax group and a customers company tax group.

When importing an order the system will look up the tax matrix and see if there is a tax code for the given product tax group and  company tax group. If there is then it will use this tax code rather than the default tax code.

Please check with the client that if the are using tax matrix's and are they set up.

If the wrong Tax group is setup you may get an error message

Error #1 importing Order Number '484967'. Ostendo failed : <?xml version="1.0" encoding="utf-8"?>  <ostendoapi>  <ostendoapiversion></ostendoapiversion>  <status>error</status>  <value>exception 104  NOSUCHLOOKUPVALUE  There is no such No Such TAXGROUP TAXABLE  At procedure 'LOOKUP_VALIDATION' line: 75, col: 15 At trigger 'SALESHEADER_REQUIRED'</value>  </ostendoapi>  

Go to the Accounting system settings -> Save Sale for Ostendo

Change the Tax group to match Clietns -> E.G