When contractors bill owners or GCs on an AIA document, the Application numbers are sequential within the job. For instance, project 123 is billed in three progress billings. They would be Application 1, Application 2 and Application 3. Project 789 will also have multiple pay applications which need to restart with one. This sequence helps keep the subcontractor & owner/GC in agreement with how much has been billed and how many bills have been submitted for the project.
A bonus would to be able to segment the reference number and have the first segment autopopulate with the project number and the second section run sequentially. Example for project 123 is 123-001, 123-002, 123-003, etc. This is a standard way of numbering pay apps in the construction industry.