How to automate unpaid invoice reminders in Dolibarr (complete 2026 guide)
Overdue invoices cost you time and cash flow
If you run billing in Dolibarr, you know the drill: an invoice reaches its due date, payment does not arrive, and someone has to remember to follow up. Manually, it is slow, easy to forget, often too late — and cash flow suffers.
The good news: Dolibarr offers several ways to automate reminders. This guide walks through them from simplest to most powerful so you can pick what fits. We are honest about each method’s limits.
Method 1 — Dolibarr’s native Notifications module
Dolibarr includes a Notifications module that can send emails on certain events. It is the simplest starting point.
Its limits: it fires on specific events (e.g. invoice validation) but does not natively handle “X days after due date, if still unpaid”. For delay-based overdue follow-up, it runs out of steam quickly.
Useful when: you only need a simple alert on validation or a single event. Not enough when you want automatic follow-up based on how long an invoice has been overdue.
Method 2 — Native scheduled task for reminders
Recent Dolibarr versions offer a cron job dedicated to sending reminders for overdue customer invoices. That is one step up.
You configure a daily cron job that emails when an invoice is past due by a configured number of days. No code required.
Its limits: logic stays relatively rigid (one day offset, one email template). As soon as you want staggered reminders (D+8, D+15, D+30) with different messages, amount or customer-type conditions, or chained actions (create a follow-up task, notify a sales rep), you hit the ceiling of native configuration.
Method 3 — Custom PHP trigger
For advanced logic, the classic approach is a custom Dolibarr trigger: PHP that reacts to events and sends reminders under your rules.
Powerful and fully flexible — but also: code to write and test, developer skills, maintenance on every Dolibarr upgrade, and logic invisible to daily ERP operators (it lives in PHP files). For many businesses, that means hiring a contractor.
Method 4 — Visual workflow editor: Knot Core
If you want code-level flexibility without writing code, a visual workflow editor helps. Knot Core is a free, open-source (GPL) Dolibarr module that adds a canvas inside Dolibarr to build automations visually — nothing leaves your server for a vendor cloud.
Here is how to build staggered overdue reminders with Knot Core.
The trigger. Place a Cron trigger on the canvas, scheduled daily. It checks invoice status every day. See Cron trigger.
Fetching invoices. With the Dolibarr connector, fetch unpaid customer invoices past their due date. See Dolibarr connector.
Reminder logic. With the Logic connector, branch by age: 8 days overdue, 15 days, 30 days. Each branch can send a different tone — polite reminder to firmer follow-up. See Logic connector.
Sending email. With the Email connector (free in Knot Core), send the matching reminder with invoice variables (reference, amount, due date, customer name) in the body. See Email connector.
Optional follow-up actions. Chain more nodes: create a task, notify the account owner, log the send.
Test before going live. Use Simulate first: the workflow runs dry — no real emails, no DB writes. Read the execution timeline, confirm the right reminder fires at the right time, then activate. See Simulate.
Once live, every run is tracked in Track runs with status so you can audit what went out. New to Knot? Start with Your first workflow.
Which method to choose?
Simple notification on an event: native Notifications is enough.
Single delay-based reminder without advanced needs: native scheduled task works.
Staggered, conditional reminders with chained actions — and no coding: a visual editor like Knot Core is the best balance of power and accessibility. Because it is self-hosted, customer data never leaves your server, unlike cloud tools such as Zapier.
Try without installing
See Knot Core on an online demo: create a test account at https://knot.tools/en/try/ and explore the canvas.
To install on your Dolibarr instance, Knot Core is a free download at https://knot.tools/en/ — open source (GPL), no activation code.
Knot Core is in beta: usable and already adopted; your feedback helps it improve.
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