Automate client follow-up without sending messages out of place

A client going months without buying does not explain why. They may not need the service, have an appointment pending or have decided to change provider. I would start by checking those statuses before preparing a message sequence.

The last purchase date helps find records to review. It does not make every person in those records a campaign recipient, nor does their number multiplied by average spend represent recoverable revenue.

First, what you want to communicate and through which channel

Confirming a booked appointment and encouraging someone to buy another service have different purposes. A reactivation message inviting a booking is commercial even if you call it a “reminder” or use a friendly tone.

In Spain, article 21 of the LSSI-CE prohibits advertising or promotional communications by email or equivalent channels that have not been requested or authorised. It provides an exception for a previous contractual relationship where contact data were obtained lawfully and the offer concerns the business's own products or services similar to those previously contracted. In all cases, it requires a simple, free opt-out when data are collected and in every communication. Article 21.

A phone number on an invoice would not be enough. If you choose WhatsApp, its policy requires the person to have provided the number and given permission to receive subsequent messages; it also requires respecting withdrawal. On WhatsApp Business Platform, starting conversations requires approved templates, and outside the 24-hour service window only those templates may be sent. WhatsApp Business policy. A contractual relationship that may permit sending under the law does not replace the platform's requirements.

When records contain personal data, you also need to define the processing purpose and legal basis, limit the data and honour objections to direct marketing. The GDPR sets out those principles and that right in articles 5, 6 and 21. General Data Protection Regulation.

The workflow needs more than a date

I would record the last service, next appointment or order, channel, permitted purpose, evidence of permission where relevant, last message and opt-out status. The information must be current before assessing a send, not only when the list was imported.

The system can suggest candidates and exclude pending appointments, open complaints, opted-out contacts and recent messages. Initially, I would review that list manually. This lets you find a reasonable threshold from your own service frequency instead of copying a table of sectors.

In a hypothetical maintenance example, the timing would be based on the interval agreed with the client and the service performed. I would not assume 90 days means inactivity for everyone. If the next service depends on usage, you need that information or must ask, without presenting a check as overdue when it is not.

A reply must change the status

An initial message can identify the business, explain the reason for contact and offer a specific action. If it is commercial, include the simple opt-out route. Do not claim there are slots this week if the system has not checked the calendar.

If the client replies, pause the sequence and assign the conversation to a person. If they ask to stop receiving messages, record the withdrawal and check that it also blocks sends already queued. If they do not reply, I would start with a single contact, without automatically scheduling three attempts.

Automating selection does not eliminate replying, correcting data and supervising failures. I would measure total time, useful replies, opt-outs and services ultimately booked. Those results let you adjust the follow-up; a long list of former clients alone does not demonstrate an economic opportunity.