Receipt (orderid) Numbers
When the shopping cart is installed, the first orderid number will begin at 1. New orderid numbers will then auto increment from the highest existing orderid number in the orders database table each time a new order is created.
The beginning orderid number can be increased using a database management tool such as phpMyAdmin. Most hosting services provide phpMyAdmin. In Plesk it is called DB WebAdmin.
Browse the database table named orders.
Either add a row with the higher orderid number or, if the highest existing orderid number is not needed for anything else (for instance it is an incompleted/unpaid or a test order), change the highest orderid to the higher number and save the change (click Go).
Subsequent new orders will then auto increment to higher orderid numbers.