Passport365 automatically creates a three-character prefix based on the first three letters of your company name that will be used on your company quotes, jobs and invoices. 

As an example, if your company was called Johns smith heating, your three-character reference would be JOH. 

You can change this to anything you want from within the company settings page.
It doesn't have to be three characters (it can be more or less). 

Once you have updated your characters in the "reference prefix box" click save at the bottom of the page.
Note: All of your existing quotes, jobs and Invoice references will be updated with your new characters

Now all of your job, quote and Invoice references will be updated with your new prefix