Hi,
You have not followed the instruction in my above reply with thread in it.
You can use tax code Z3 in your PO which have 0% Excise + 4.2% VAT
You can create new tax code Z4 with Excise %(matching your entered in MIGO + 4.2% VAT)
How client not aware of tax % where all taxes are calculated and charged on % basis which is easy to monitor and replicate.
You need to explore, map and complete the process either use available tax code {excise %+ 4.2%VAT} or create a new tax code for excise % + 4.2% VAT to carry out invoice verification.
Regards,
Biju K