Diagnosis
For One cycle grossing up, the system require the base item tocalculation the final withholding tax. There are 2 withholding taxitems in the document with same WT code. The base item must have 100%tax base and the supplement item must have the tax base and rate equalto the rate from base item.
For example: in the document, there are 2 w/tax types per onevendor/customer item
WT type WT code Tax base Tax rate
J1 10 ,, 100% 5% <--- Base item
J2 10 5% 5%<--- Supplement item

System Response
The certificate can be generated with this warning.