such transaction should be avoided. hence should not be recorded.

yes we can do this in Tally ERP 9. businesses normally use zero values when giving away samples or when they offer promotional schemes like 'buy 3 get 1 free'. there may also be other legitimate reasons.

to enable this feature, from Gateway of Tally press F11. then Press F2 or select Inventory Features. In General (heading) set YES to the option ' Allow Zero valued entries'.

hope this helps. if you need more help let me know.