In the UK and across Europe, one in three SMBs waits more than 30 days past the due date to receive payment on their overdue invoices. The average cost: €4,200 of frozen cash flow per month for a 10-person team, with an average payment delay of 47 days. And the chasing? Between 45 minutes and 2 hours every week — for mediocre results, because you always put it off.
An AI agent configured on n8n + Claude API solves this problem in 4 hours of setup, for €25–40 per month.
Key Takeaways
- Total cost: €25–40/month (n8n Cloud ~€20 + Claude API €5–15 + Brevo free)
- Setup: 4 hours maximum, no technical skills required
- Cash flow gain: €3,000–8,000 over 3 months (SMB average)
- Payment rate at D+7: 58–72% with the AI agent vs 31% with manual chasing
- Time recovered: 1h30–2h per week
- GDPR: Compliant if EU-hosted (OVH/Scaleway) + Claude API stateless + Article 30 register
- Compatibility: Pennylane, Sellsy, QuickBooks, FreeAgent, Xero (or manual Google Sheets)
- Not suitable for: <10 clients/month, public contracts, frequent disputes, unstructured invoice list
Why manual follow-ups fail (and cost more)
Invoice chasing is a textbook case for automation: it's repetitive, follows clear rules, and every hour of delay has a measurable financial cost.
The problem isn't a lack of willpower. It's context. When you're finalising a quote, handling an unhappy client or preparing a presentation, chasing a €1,500 invoice drops to the bottom of the list. Then it's D+7. Then D+15.
The numbers speak for themselves:
| Method | Payment rate at D+7 post-chase | Weekly time |
|---|---|---|
| Manual follow-up | ~31% | 1h30–2h |
| Automated AI agent | 58–72% | ~5 minutes (supervision) |
The difference doesn't come from AI magic. It comes from mechanical consistency: the agent never procrastinates, never feels awkward about sending a follow-up email, and adapts the tone to the delay without effort.
What the agent actually does — step by step
The agent monitors your invoice list continuously. As soon as an invoice becomes overdue, it triggers a precise sequence:
1. History check — have we already chased this client? When?
2. Tone selection appropriate to the delay (cordial at D+1, direct at D+7, firm at D+15)
3. Email generation via Claude API, personalised with the client's name, amount and invoice reference
4. Sending via Brevo (or your SMTP)
5. Status update in Google Sheets + action log
6. Slack or email alert if an invoice reaches D+21 without a response
You only intervene on complex cases — strategic clients, disputes, phone calls. Everything else is handled without you.
The stack — technical choices and why
n8n: the no-code orchestrator
n8n is an open-source automation platform with a visual interface. Unlike Zapier or Make, it can be hosted in Europe (OVH, Scaleway), which simplifies GDPR compliance.
Claude API: email generation
Claude API (Anthropic) generates follow-up emails from a structured prompt. Key advantage: the model produces natural, non-robotic emails adapted to context — something a static template cannot do.
Real cost: €5–15/month for an SMB with 20 to 80 active invoices.
Brevo + Google Sheets
Total budget: €25–40/month. For an average cash flow gain of €3,000–8,000 over 3 months.
Building the workflow — 5 steps
Step 1 — Prepare the data source
Create a Google Sheet with these columns:
`````
The Status field accepts three values: Pending, Chased, Paid. This is the field n8n reads to decide whether to act.
If you use Pennylane, Sellsy or QuickBooks, check whether your plan includes an API — n8n can read these tools directly without going through Sheets.
Step 2 — Configure the automatic trigger
In n8n, create a workflow with a Schedule Trigger node set to Every day at 8:00 AM.
This node triggers reading your Sheets file, filters rows where Status = "Pending" and Due date < today, then calculates the exact delay in days.
Step 3 — Generate the email with Claude
For each overdue invoice, n8n calls the Claude API with a contextual prompt that adapts the tone to the delay. Here is an operational prompt example:
`
You are the accounting assistant for a small business.
Write a payment reminder email for an overdue invoice.
Client: {{client_name}}
Amount: {{amount}}€
Days overdue: {{delay_days}}
Invoice reference: {{invoice_number}}
Tone rules:
Generate the subject line and email body. No signature, no generic opening formula.
`
Claude returns the subject and body. n8n passes them to the Brevo node.
Step 4 — Sending and traceability
The Brevo node sends the email from your professional address. Immediately after, n8n updates Google Sheets:
→ today's date → Chased → incremented by 1A conditional node checks if Follow-ups count >= 3 or Delay > 21 days`. If so: Slack or email notification to you for manual handling.
Step 5 — GDPR guardrails
Three rules to follow:
Client data does not leave your Google Workspace environment. The only external flow is the prompt sent to Claude API, which contains only the name, amount and delay — not the email address or sensitive information.
Results measured on deployed SMBs
On SMBs that activated this type of workflow for at least 60 days:
Return on investment is immediate: at €40/month cost, a single automated follow-up that accelerates a €500 payment makes the system profitable for that month.
Cases where this workflow is not suitable
This system is not right if:
In these cases, automation can apply to a subset of your client portfolio (standard invoices) and exclude complex cases via a filter in Google Sheets.
To get started this week
The workflow can be live in 3–4 hours:
1. Create your Google Sheet with the columns listed in step 1
2. Sign up for n8n.cloud (Starter plan, ~€20/month)
3. Create a Claude API account at console.anthropic.com — top up €20 to start
4. Open a Brevo account free for email sending
5. Build the workflow following the 5 steps above
The first automatic follow-up will go out the next morning at 8 AM.
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Learn more
💡 Neuraweb deploys this type of AI agent in under a week, with integrated human oversight and documented GDPR compliance. If your use case is more complex (multi-currency, specific CRM, advanced sequences), let's talk directly →
FAQ
How much does an AI agent to automate invoice chasing cost?
The total cost is €25–40 per month: n8n Cloud at ~€20/month, Claude API at €5–15/month depending on email volume generated, and Brevo free up to 300 emails/day. Self-hosted, n8n is free — only the Claude API cost remains.
Do you need technical skills to set up this workflow?
No. n8n is a no-code/low-code platform with a visual drag-and-drop interface. The basic setup (Google Sheets connection, daily trigger, Brevo sending) requires no coding. Claude API integration means copying an API key and writing a prompt — about 30 minutes of work.
Can the AI agent handle phone follow-ups or disputes?
No, and this is intentional. The agent only handles email follow-ups on standard invoices (D+1, D+7, D+15). Once an invoice passes D+21 without a response, the system sends you an alert for manual handling. Strategic clients, disputes and specific protocols remain under your control.
Is this workflow GDPR-compliant?
Yes, provided you respect three rules: host n8n on a French or European server (OVH, Scaleway), use Claude API in stateless mode (Anthropic does not retain your data between calls), and mention automated processing in your GDPR processing register (Article 30). Client data does not leave your Google Workspace environment or your server.
Which billing software is compatible with this workflow?
Any tool that exposes an API or allows export to Google Sheets is compatible: Pennylane, Sellsy, QuickBooks, FreeAgent, Xero. Without a direct API, a simple Google Sheet updated manually each week is enough — n8n reads it and triggers follow-ups automatically.