# AI Invoice Collection Agent An AI agent that monitors unpaid invoices, sends timely reminders, handles replies about payment status, and escalates overdue accounts — keeping your cash flow on track. ## The Problem Chasing unpaid invoices is one of the most tedious and important tasks in any business. Late payments are the norm — the average B2B invoice is paid 8 days late, and nearly a quarter go over 30 days past due. Every day an invoice sits unpaid is a day your cash flow suffers. The process is maddening in its repetitiveness. Someone on your finance team has to check which invoices are approaching their due date, compose a polite reminder, send it, wait for a reply, and follow up again if nothing happens. Multiply this across dozens or hundreds of outstanding invoices and it becomes a full-time job — one that most companies handle inconsistently because nobody wants to be the person sending awkward payment reminders. The human side matters too. Invoice follow-ups are conversational. A client might reply saying they have sent payment, ask for a copy of the invoice, dispute a line item, or request a payment plan. These replies need to be read, understood, and acted on — not just logged in a spreadsheet. ## How an Agent Solves This An AI invoice collection agent automates the entire follow-up cycle while keeping the communication personal and conversational. The agent monitors your accounts receivable, sends reminders on a schedule, and handles the back-and-forth that follows. Here is how it works: - Agent checks your billing system daily for invoices approaching their due date or past due - Sends a friendly reminder 3 days before the due date, with a link to the invoice and payment details - If the client replies — confirming payment, asking a question, or disputing — the agent reads the reply and responds appropriately - If no payment or response after the due date, the agent sends a firmer follow-up and CC's your finance team - Severely overdue invoices are escalated to a human with the full communication history and recommended next steps The agent maintains a professional, consistent tone across all communications. It never forgets to follow up, never sends a reminder on the wrong date, and never loses track of who said what in a payment conversation. ## How It Works with Robotomail Robotomail provides the email infrastructure for your collection agent: a dedicated billing mailbox, outbound sending with proper authentication, inbound reply handling via webhooks, and thread tracking to keep each invoice conversation organized. ### 1. Send payment reminders Your agent sends reminders from a dedicated billing address like `billing@yourcompany.com`. Each email is properly signed with DKIM and SPF so it lands in the inbox, not spam. Send payment reminder ``` # Agent sends a payment reminder curl -X POST https://api.robotomail.com/v1/mailboxes/mbx_billing01/messages \ -H "Authorization: Bearer rm_live_abc123" \ -H "Content-Type: application/json" \ -d '{ "to": ["ap@clientco.com"], "subject": "Friendly reminder: Invoice #1042 — $8,400 due March 28", "bodyText": "Hi, This is a friendly reminder that Invoice #1042 for $8,400.00 is due on March 28, 2026. Payment details: - Amount: $8,400.00 - Due date: March 28, 2026 - Invoice: https://billing.yourcompany.com/inv/1042 If you have already sent payment, please disregard this message. Otherwise, let me know if you have any questions about this invoice. Best regards, Billing Team", "bodyHtml": "

Hi,

This is a friendly reminder that Invoice #1042 for $8,400.00 is due on March 28, 2026.

" }' # Response { "id": "msg_4n8k1x", "threadId": "thr_7v2p5q", "status": "sent", "sentAt": "2026-03-22T08:00:00Z" } ``` ### 2. Handle replies When a client replies to a reminder, Robotomail delivers the message to your agent via webhook. The agent can parse the response — did they confirm payment, ask a question, or raise a dispute? — and respond accordingly. Client reply webhook ``` # Client replies — Robotomail delivers via webhook { "event": "message.received", "data": { "id": "msg_6m3j9w", "mailboxId": "mbx_billing01", "from": { "email": "ap@clientco.com", "name": "Lisa M." }, "subject": "Re: Friendly reminder: Invoice #1042 — $8,400 due March 28", "text": "Hi, we have processed the payment via wire transfer this morning. Should arrive in 2-3 business days. Can you send us a receipt once it clears?", "threadId": "thr_7v2p5q", "receivedAt": "2026-03-22T14:20:00Z" } } ``` ### 3. Continue the conversation The agent replies in the same thread, keeping the conversation organized. It can also update your billing system — marking the invoice as "payment pending" when a client confirms they have sent a wire, for example. Agent acknowledgment ``` # Agent acknowledges and updates internal status curl -X POST https://api.robotomail.com/v1/mailboxes/mbx_billing01/messages \ -H "Authorization: Bearer rm_live_abc123" \ -H "Content-Type: application/json" \ -d '{ "to": ["ap@clientco.com"], "subject": "Re: Friendly reminder: Invoice #1042 — $8,400 due March 28", "inReplyTo": "", "bodyText": "Thanks Lisa, I have noted the wire transfer. I will send a receipt as soon as the payment clears on our end. If it has not arrived by March 27, I will follow up. Appreciate the quick response.", "bodyHtml": "

Thanks Lisa, I have noted the wire transfer. I will send a receipt as soon as the payment clears on our end...

" }' ``` ### 4. Escalate overdue invoices For invoices that remain unpaid after multiple reminders, the agent escalates with a firmer tone and CC's your finance team. Custom headers let your systems track escalation status programmatically. Escalate overdue invoice ``` # Agent escalates overdue invoices with context curl -X POST https://api.robotomail.com/v1/mailboxes/mbx_billing01/messages \ -H "Authorization: Bearer rm_live_abc123" \ -H "Content-Type: application/json" \ -d '{ "to": ["ap@clientco.com"], "cc": ["finance@yourcompany.com"], "subject": "Overdue: Invoice #1038 — $12,600 (14 days past due)", "bodyText": "Hi, Invoice #1038 for $12,600.00 was due on March 8 and is now 14 days past due. I have sent two previous reminders on March 5 and March 12. Could you provide an update on the payment status? If there is an issue with the invoice, I am happy to help resolve it. Invoice: https://billing.yourcompany.com/inv/1038 I have CC'''d our finance team for visibility. Best regards, Billing Team", "headers": { "x-custom-invoice-status": "overdue", "x-custom-days-past-due": "14" } }' ``` ## Key Benefits - **Consistent follow-up.** Every invoice gets the right number of reminders at the right time. No invoices fall through the cracks because someone was on vacation or forgot. - **Conversational handling.**Unlike notification-only tools, the agent reads and responds to client replies. If someone says "we sent payment yesterday," the agent acknowledges it and updates your records. - **Professional sender identity.** Emails come from your company domain with proper DKIM and SPF authentication. Reminders land in the inbox, not the spam folder. - **Graduated escalation.** The agent adjusts tone based on how overdue an invoice is — friendly reminders before the due date, firmer follow-ups after, and human escalation for severely past-due accounts. - **Full audit trail.** Every message is stored with thread context. Your finance team can review the complete communication history for any invoice at any time via the [threads API](https://robotomail.com/docs). Check the [API documentation](https://robotomail.com/docs) for webhook setup, threading, and custom headers. Read [why we built Robotomail](https://robotomail.com/blog/introducing-robotomail), or [sign up free](https://robotomail.com/sign-up) and have your invoice agent running by end of day.