Tax Code error

Hi Experts

I created a billing  document with the below two taxes.

MWST - Copied from sales order

ZEEX - Excise duty - Added manually in billing document.

I get the message when I try to post the invoice to billing document."Error in account determination: table T030K key ABCD ZEX; Message No. Message no. FF709 "

The tax code is not determined when I entered the excise duty manually in the billing document. How can I have the tax code determined automatically. I can confirm that all FI tax settings for this condition type are in place.

Please help resolve this issue.

Thanks