- Billing forms or electronic processing systems such as Textura
- Notarization of billings
- Certified payroll
- Lien releases
- Other backup for the billing including invoices if it is a T&M or GMP project
You will need these documents from both your own company and likely from your subcontractors and key vendors. Make sure that you have the requirements for all these in their terms and conditions.
Build relationships with everyone in the workflow who is responsible for reviewing and approving your billings for contractual compliance not forgetting outside auditors.
If you aggressively bill and get approvals for the progress billing amounts then this contract compliance backup is the last thing that can hold up getting paid.