How do I turn on automatic payment reminders and why is it sometimes blocked?

Payment reminders to the client (an advance notice before the due date and an overdue notice) are OPT-IN: the agency turns them on with a checkbox in the payment plan, so no automatic emails go out unintentionally. Also, they can't be enabled without a collection method set up (Stripe gateway or IBAN for transfer): you'll see a notice telling you to set up collection first.

1. 1In the proposal's (or group's) payment plan, tick «Automatic reminders to the client».
2. 2If you have no gateway or IBAN, you'll see a notice: set up collection in Settings → Payments.
3. 3With collection set up and the checkbox on, the client gets the advance notice (7 days before) and the overdue one.

Consejo: If you leave the checkbox off, no automatic reminder is sent to the client (the internal notice to your team stays). It's a per-proposal/group decision.