Allow 2 type of auto-generating invoice numbers

Allow 2 type of auto-generating invoice numbers

Dear ZOHO Team,

Kindly allow 2 type of auto-generating invoice numbers

Because I am air Ticketing agent & I have created 2 type of invoice 

for example, 
Tax invoice start with INV-000001
Out of scope invoice start with DM-000001

So it most important for our business