Do not wait too long to follow up: a fixed escalation sequence improves your chances of payment and protects your legal position. Document every step in writing.
Step 1: reminder
Send a friendly reminder 1 day after the due date with invoice number, amount and payment instructions.
Step 2: second reminder
After 14 days, send a more formal reminder and state that you will issue a formal demand if payment is still missing.
Step 3: formal demand
Send a notice of default (Dutch: ingebrekestelling/aanmaning) with statutory interest, collection costs if applicable and a new payment term (e.g. 14 days).
Step 4: debt collection
Engage a collection agency or start proceedings at the subdistrict court (kantonrechter, claims up to €25,000). Keep all correspondence.
Prevention
Use clear contracts with payment terms, work with a service agreement (overeenkomst van opdracht) and use SmartWerk: payment-due-soon from the invoice list (BASIC+), overdue recovery in Reminders (PRO+, automatic on PREMIUM).