invoice no is mandatory only 16 digits

it is upto 16 digits 

m tell u the max dighit u can use that is 16 

invoice no always minium so that u can remember also 

and not require to take time while doing entry 

simple way compair ur invoce no with others 

ask ur vendors what problems they  with inovice no 

u will get ur problem solved

in my view invoce no should be minium 

not more than 8 to 9 dight like first invoice of november  - 1 /2017-18