Automatic Reminders Disabled: For a customer to receive SMS reminders for visits, they need to have automatic reminders enabled. This feature is enabled by default for each customer, but it might have been turned off by someone. To check, you can edit the contact and ensure the "RECEIVES AUTOMATIC VISIT REMINDERS" checkbox is ticked.

Missing Mobile Phone Number: Another reason a contact might not receive SMS reminders for visits is a missing mobile phone number. It's not enough to add a mobile phone number to the regular phone number field, as we only send reminders to contacts who have a mobile phone number set.