Phone System · 2 min read
Error 21606: "From" Number Is Not SMS Capable
What this error means
Error 21606 (often shown as "From number is not SMS capable") means the number or sender used in the From field can't send this message. The sender must be active in your sub-account and must support SMS for the destination you are texting.
Not every number can text. Voice-only numbers, some toll-free numbers that still need verification, and numbers that are still being ported can't send SMS.
Common causes
- The sending number is voice-only.
- The number is not in the current sub-account, or was released.
- The number is still being ported and isn't fully active.
- A short code is being used for a recipient in another country.
- The number is not fully provisioned or registered yet.
- A workflow, campaign, or user default is still pointing to an old number.
Check whether a number supports SMS
- Go to Settings → Phone System → Phone Numbers.
- Find the sending number.
- Review its capabilities and confirm SMS is listed.
- If SMS is not listed, use a different number or buy an SMS-capable number.
How to fix it
- Confirm the number is active and owned by this sub-account.
- If it is being ported, wait until the port is complete before texting from it.
- If it is a toll-free number, make sure toll-free verification is approved.
- If it is a US local number, make sure it is linked to an approved A2P campaign.
- Set an SMS-capable number as the default sending number.
Update workflows and automations
Open each workflow that sends SMS and check the From number in the Send SMS action. Replace any voice-only or removed number. Also check user-level default numbers under Settings → Phone System, because a user's default can override the location default in conversations.