We don't see message errors frequently, but here are a few of the common error messages you might see and what they mean.
Unknown destination handset - The destination number you are trying to reach is unknown and may no longer exist.
Landline or unreachable carrier - The destination number is unable to receive this message. Potential reasons could include trying to reach a landline or an unreachable carrier.
Customer unreachable by SMS - this Contact has replied to one of your messages with one of the industry standard SMS unsubscribe commands. They will need to reply again with START or YES in order to receive any further messages from you. Alternatively, the Contact could have been unsubscribed by an agent. Go to the Contact’s profile page to see if re-subscribing them is an option. Make sure to have their consent before re-subscribing them to your messages.
Blocked - someone in your organization has marked the customer as Blocked. You will not receive any notifications from messages this customer sends in and the message will not be moved to the top of your Conversation List if there is new activity. They will still be able to text you and you can still respond.
Carrier violation - Your message was flagged as objectionable by the carrier. In order to protect their subscribers, many carriers have implemented content or spam filtering. Carriers do not provide us with any additional information as to why a particular message was flagged, but you should still be able to send other messages to the contact.