Click Users on the left navigation bar, followed by Field rep. Click on the the sales rep user, and then click the Assign invoice number link located on the top screen.
Enter the prefix, initial and last number.
The prefix is an alphanumeric phrase that starts all invoice names for a given field rep. For example, the user s1@insitumobile can opt to have his invoices set to prefix S1-.
The initial number is the value to start invoices. For example, you could set it to 5000 if you wanted the first invoices for s1 to be S1-5000.
Enter the last number (last number to be assigned). Most of the time, web users don't have a limit in mind, so you can use a large number like 9999999.
Go to Integration: Quickbooks on the left navigation menu and find the option Invoice Number.
Change it to Use inSitu Sales invoice Number and hit Save Settings.
MAKE SURE THE MOBILE USER SYNCS THE APP.