I’m using a tablet, and the messages are not getting sent

On the Basic and Premium plan, the messages are sent from your device. Since tablets do not have or support a carrier connection, the messages won’t work. 

To send messages to all clients using a tablet, you need to upgrade to Ultimate. On the Ultimate subscription, the reminders are sent automatically using our cloud messaging system. The messages are sent from a generic phone number from your area.

More information about the Ultimate plan, you can find here.