For order management, you need a number range object which provides you with order numbers. This number range object must have exactly one number range interval, which is numbered '01'. You must not flag the 'external' field.
Interval: 01
From number: 10000
To number: 999999
Current number: 10000
External: not flagged
SAP recommends that you start the order number interval with a five-digit number, such as 10000.
Define number range interval 01.