# 63015: Channel Sandbox can only send messages to phone numbers that have joined the Sandbox

Log Type: APPLICATION

Log Level: ERROR

## Description

Channel Sandbox can only send messages to phone numbers that have joined the Sandbox

### Possible causes

This message failed to be delivered to the user because it was sent from a Sandbox to a phone number that has not joined your Sandbox

### Possible solutions

Instruct the recipient to join your Sandbox by sending the join phrase or keyword shown on the Sandbox page in your Twilio Console.