Begin with the governing contract records
Create one file for the executed contract, purchase order, notice to proceed, amendments, and approved change orders. Confirm which document controls billing frequency, format, rates, retainage, milestones, and submission method. Illinois vendors should also keep their registration and business information current where the applicable procurement process requires it. The Illinois Procurement Gateway collects business information used by vendors working with State agencies and universities.
Match the invoice to the purchase order
Use the exact legal business name, remit-to address, purchase order number, contract number, agency or department, and billing contact shown in the government record. Invoice numbering should be unique and consistent. Check service dates, quantities, units, hourly rates, taxes, credits, and totals against the authorized terms. A small mismatch can send an otherwise valid invoice into an exception queue.
Prove delivery and acceptance
Attach the evidence required for the specific contract: signed delivery receipts, timesheets, inspection records, progress reports, milestone acceptance, certified payroll, photographs, or completion letters. Label each item clearly and connect it to the invoice line it supports. If a subcontractor or project manager supplied the proof, preserve the original record and the date it was received.
Confirm approvals and submission instructions
Check whether the jurisdiction requires a project manager signature, department approval, portal upload, email subject format, vendor certification, or separate backup file. Verify file-type and size limits before submission. Name digital files consistently so both your team and the reviewer can identify the vendor, invoice, contract, and billing period without opening every attachment.
Run a final pre-submission review
Have someone other than the preparer compare the invoice with the contract and supporting documents. Confirm all pages are readable, totals reconcile, attachments are complete, and confidential data is handled through an approved channel. Save a locked copy of the final package, submission confirmation, date, recipient, and follow-up schedule. This repeatable invoice-readiness checklist creates a cleaner audit trail and reduces preventable rework.
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