What is the legal basis for sending SMS?
There are various legal bases which may authorise you to send SMS.
It is advisable to obtain the consent of your recipients before sending SMS messages. To be on the safe side, we also recommend that you use a double opt-in. The first message you send to your new recipients should therefore be a request for confirmation of consent. If the recipient does not agree again, you should not send any further SMS to this recipient.
You can read more details about this in our blog post.