If you received an error code 4720, it means the recipient's carrier has rejected the message due to an invalid destination address.
Possible reasons
The number is not in the numbering plan (the area code doesn't exist or the number is just invalid) or it's not enabled for messaging (like a landline).
An issue with the recipient's handset may have prevented message delivery.
For T-Mobile traffic, the recipient may have opted out of receiving toll-free and short code messages.
Actions to resolve
Handset issues can be temporary. Retest by sending the message again.
For T-Mobile traffic, ask the recipient to remove Content Blocking if they want to receive messages from your number.
Troubleshooting
If the issue persists, please open a ticket with Bandwidth Support and provide more details (message content, time of day, etc.) so we can investigate further. For the full list of messaging error codes, please see our dev docs.