A sent invoice may still be waiting outside the approval process

"Sent" means your system attempted delivery. It does not prove that the customer's accounts payable team accepted the invoice for processing.

Elite's research highlights billing-process friction at large law firms.^[1] Smaller service businesses should investigate their own experience rather than borrow that study's statistics, but the distinction between delivery and acceptance is useful at any scale.

Check whether the customer requires a portal, a purchase order, a timesheet or an operational approval. Retain submission confirmation and the rejection reason where available. If acceptance is not explicitly reported, label the status unknown; do not infer it from an email open.

Consider an invoice emailed to the project sponsor when the buyer requires portal submission. More reminders to the sponsor may not move it into the payable queue. Correcting the submission route is the actionable fix.

Measure the share accepted without rework among invoices with known outcomes, and show the pending group separately. That avoids manufacturing an impressive acceptance rate from incomplete information.

Use the billing readiness checklist to prevent repeat rejection and reason-based follow-up when the invoice remains unpaid.