Twilio · api · fg-0160

Error 21610 after a recipient texts STOP, and the API cannot override it

21610 Attempt to send to unsubscribed recipient

Verified 2026-10-15 · Confirmed by 0 builders · Trust 50/100

Cause

Twilio processes STOP and the other opt-out keywords itself and blocks further messages from that sender or Messaging Service until the person texts START.

Fix

Catch 21610, record the contact as opted out, and stop retrying. Only the recipient can lift it by texting START.

Apply

try {
  await client.messages.create({ from, to, body });
} catch (err) {
  if (err.code === 21610) await markOptedOut(to); else throw err;
}

Affects: Twilio Programmable Messaging default opt-out handling, checked October 2026

Sources

https://www.twilio.com/docs/api/errors/21610

Have your agent know this before it fails

claude mcp add --transport http footgun https://getfootgun.com/api/mcp