The Agentic AI Playbook: Build an Invoice Follow-Up Agent That Chases Late Payments

Late invoices are one of the most predictable cash flow problems a small business faces, and one of the least automated. Most owners either let overdue invoices sit too long (to avoid the awkwardness) or chase them manually in a way that’s inconsistent and time-consuming. An invoice follow-up agent handles the grunt work and keeps the pressure on without you having to do anything.

Here’s how to build one.

What the agent does

The agent monitors your invoicing system for overdue invoices and sends a timed sequence of follow-up emails. It personalises each message with the client’s name, the invoice amount, and the due date. It stops the sequence automatically when the invoice is marked paid. You don’t think about it until you need to.

When to trigger

Set the trigger logic based on days past due, not calendar dates.

On day one, send a polite reminder. Assume the missed payment was an oversight. On day seven, follow up again, a little firmer, noting that payment still hasn’t been received. On day 14, shift to a final notice tone. Make it clear the invoice is now two weeks overdue and you need payment that week.

At 30 days, stop the automation entirely. After that, you need a conversation.

The email sequence

Here are three templates that work. Adjust the voice to fit your business.

Day 1: polite nudge

Subject: Invoice [#NUMBER], just checking in

Hi [First Name],

Wanted to check in on invoice [#NUMBER] for $[AMOUNT], which was due on [DATE]. If it’s already been sent, please ignore this. If not, the details are attached.

Let me know if you have any questions.

[Your name]

Day 7: follow-up

Subject: Invoice [#NUMBER], now 7 days overdue

Hi [First Name],

Following up on invoice [#NUMBER] for $[AMOUNT], now 7 days past due. I haven’t received payment yet. Could you let me know when this will be processed?

If there’s an issue with the invoice, let me know and we can sort it out.

[Your name]

Day 14: final notice

Subject: Invoice [#NUMBER], 14 days overdue, payment required this week

Hi [First Name],

Invoice [#NUMBER] for $[AMOUNT] is now 14 days overdue. I need payment this week to avoid escalating this further. Please arrange payment or contact me directly to discuss.

[Your name]

These are plain, direct, and don’t sound like a robot wrote them. That’s the goal.

Tool options

Xero has native invoice reminders built in (Settings > Invoice Reminders), which handles the basic sequence without needing a third-party tool. Most Australian small businesses are already on Xero. If you want more control over the copy or want multi-channel follow-up (email plus SMS), pair it with Zapier.

MYOB + Make.com works similarly. Use the MYOB trigger in Make.com to watch for overdue invoices, then run a scenario that sends the right email based on days past due.

Chaser is a dedicated accounts receivable tool that plugs into Xero, QuickBooks, and MYOB. It handles the full sequence automatically, lets you set custom schedules per client, and tracks opens and replies. Pricing starts around $50/month USD. If AR is a persistent problem in your business, this is worth the cost.

FreshBooks has built-in automatic late payment reminders with customisable copy. If you’re already on FreshBooks, use this before building anything in Zapier.

How to set it up in Xero

1. Go to Settings > Invoice Settings > Invoice Reminders
2. Turn on reminders and set your schedule (Day 1, Day 7, Day 14 work well)
3. Edit the default email copy to match your voice (the defaults are generic)
4. Set the “From” name to your name, not your company name
5. Test by creating a dummy invoice with a past due date and checking the preview

Done in under 30 minutes.

If you want more control: Zapier + Gmail

This approach gives you full control over the email content and lets you add SMS via Twilio or Slack notifications to yourself.

1. Trigger: Xero, Invoice Overdue (or a scheduled trigger that checks daily)
2. Filter: Only continue if invoice status is “AUTHORISED” and due date is X days past
3. ChatGPT or Claude: Pass the invoice details into a prompt: “Write a polite but firm payment reminder for a $[AMOUNT] invoice to [CLIENT NAME] that is [X] days overdue. Keep it under 80 words. Don’t sound like a template.”
4. Gmail: Send from your business address

The AI-generated copy here is the differentiator. It prevents every email from reading identically, which reduces the chance clients mentally file it under “automated.”

How to personalise without sounding robotic

A few things make automated follow-ups feel human:

• Use first names. “Hi Sarah” beats “Dear Valued Client.”
• Reference the specific invoice number and dollar amount. Vague reminders get ignored.
• Vary the subject line between emails. If all three look the same, clients learn to tune them out.
• Keep them short. Under 100 words each. Long emails signal templates.
• Drop the pleasantries. “I hope this email finds you well” signals automation instantly.

If you’re using AI to draft the copy, give it a sample of how you actually write emails. Paste two or three real examples into the system prompt as a tone reference.

What to never automate

Some payment situations need a human conversation, not a template.

Long-term clients who’ve always paid on time deserve a personal call, not a robot email, when they’re late for the first time. Disputed invoices are the same: if someone has raised a query about the work or the amount, automated reminders will make things worse. If you know a client is going through difficulty, the same applies.

Beyond 30 days, automated emails rarely move anything. At that point, you need to decide whether to write it off, offer a payment plan, or escalate.

Flag these situations in your invoicing tool with a custom tag and exclude them from the automation.

What it costs

The time saving alone justifies it. Manually chasing three overdue invoices a month, even at 20 minutes each, is an hour of work you shouldn’t be doing.

Also worth reading: What is Agentic AI? A plain-English guide for Australian businesses, which covers how agents like this one actually work under the hood.

Sources

• Xero invoice reminders: https://central.xero.com/s/article/Set-up-invoice-reminders
• Chaser pricing: https://www.chaser.io/pricing
• Zapier pricing: https://zapier.com/pricing
• Make.com pricing: https://www.make.com/en/pricing
• FreshBooks invoicing features: https://www.freshbooks.com/features/invoicing

This is part of the Agentic AI Playbook series, step-by-step guides to building AI agents that work for your business, not just answer your questions.

This guide is part of the SmallBizAI.au Automation Hub — practical automation guides for Australian small business.

More practical guides: How-To Hub →

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