Twilio errors · 2026
Twilio error 21210: “From” phone number not verified, and the two fixes for a cold caller
Last updated September 4, 2026
This is usually the second error a new Twilio account throws at a salesperson, right after the trial restrictions. You typed your office number into the caller-ID field because that is the number you want prospects to see, pressed dial, and Twilio refused with 21210. Twilio only shows a caller ID it can vouch for: a number it sold you, or one you have proved you own. Both routes take a minute; they are not equal for cold calling.
The short answer
Either buy a Twilio local number (~$1.15/month) and dial from it, or verify your existing number under Phone Numbers → Verified Caller IDs. For cold calling, buy: a Twilio-owned number assigned to your Business Profile can carry A attestation and rings the dialer on callbacks; a verified caller ID is capped at B and callbacks go to the original phone. If the number is already on “your” Twilio, it is on a different account or subaccount than the one the dialer is connected to.
The two fixes compared
| Fix | How | Cost | What you get | Fits |
|---|---|---|---|---|
| Buy a Twilio number and dial from it | Console → Phone Numbers → Buy a number → Voice → choose the area code → select it as caller ID in the dialer | ~$1.15/month per number | Inbound rings the dialer or forwards where you set; eligible for A attestation once assigned to a Business Profile; the number can be pinned to a rep | Cold calling, teams, anyone who wants callbacks in the dialer |
| Verify the number you already own | Console → Phone Numbers → Verified Caller IDs → Add → enter the code Twilio calls or texts to that phone | Free | Your existing number on caller ID; inbound stays on that phone; attestation capped at B | A solo caller who wants prospects to see the number already on their business card |
Why the error appears when the number is “already in Twilio”
Numbers and verified caller IDs belong to one account. Three situations produce 21210 on a number you can see in a Twilio console somewhere:
- The dialer is connected to a different account or subaccount. The Account SID pasted into the dialer reaches one account; the number lives on another. Reconnect with the right credentials, or move the number.
- The number was released or transferred after the dialer last loaded its caller-ID list. Reload the list; on DialSheet that is Settings → Twilio → reconnect, which re-reads the numbers on the account.
- The number was verified on one subaccount and the call is going out from another. Verification is per account. Verify it again where the calls originate.
What the choice does to attestation and callbacks
STIR/SHAKEN is how the called carrier decides whether to show “verified” or nothing. Twilio signs calls from its own numbers at level A once the number is assigned to an approved Business Profile and the SHAKEN/STIR trust product; it cannot attest a number from another provider, so a verified caller ID is signed at B at best. Callbacks follow the number too: a Twilio number rings whatever you configured, which in a browser dialer means the dialer or a forward to your cell; a verified cell number rings the cell, outside the dialer, with no recording. For a solo caller who wants one number everywhere, buy a Twilio local and forward it; see use your own phone number with a power dialer.
Neighbouring errors that look the same
- 21219 (trial, unverified recipient). The To number is the problem: a trial account can only call numbers you verified. See Twilio trial account for cold calling.
- 21217 (number does not appear to be valid). The number on your list is malformed. See error 21217 and list cleaning.
- 13227 / 21215 (geo permission). The destination country is switched off. See geo permissions.
The caller-ID picker only offers numbers Twilio will accept.
Connect your Twilio to DialSheet and the picker lists the numbers on that account; pin one per rep, forward inbound where you like, and dial at ~$0.014/min. Free for one person, $29 per 3 seats. Rather not own a number at all? A managed line is $49/month.
Start dialingQuestions people actually ask
What does Twilio error 21210 mean?
Twilio refused the call because the From number, the caller ID the call would show, is not a phone number owned by your Twilio account and is not on your account's list of verified caller IDs. Twilio will only put a number on outbound caller ID when it can attest you have the right to use it. It is not a problem with the number you are calling, and it is not a balance problem.
How do I fix error 21210?
Either buy a Twilio number and dial from that, or verify the number you want to show. To buy: Console, Phone Numbers, Buy a number, pick the area code, about ~$1.15/month; then select it as caller ID in your dialer. To verify: Console, Phone Numbers, Verified Caller IDs, Add a new caller ID, and enter the code Twilio calls or texts to that phone. For cold calling, buying is the better fix: a Twilio number assigned to an approved Business Profile can carry A attestation, while a verified caller ID is capped at B.
Can I use my cell phone number as caller ID on Twilio?
Yes, by verifying it: Twilio calls or texts a code to the phone and, once entered, the number is allowed as an outbound caller ID on that account. Two consequences for a cold caller. Inbound calls to that number still go to your cell, not the dialer, so callbacks land on your handset. And STIR/SHAKEN attestation for a verified caller ID is B at best, so the "verified" marker some phones show is less likely than from a Twilio-owned number. It works; a local Twilio number with your cell as the forwarding target usually works better.
Why did 21210 start after I moved to a subaccount?
Because numbers and verified caller IDs belong to a specific account. A number bought on the parent is not available as caller ID on a subaccount, and a caller ID verified on one subaccount is not verified on another. Transfer the number to the subaccount in Console (Phone Numbers, Manage, the number, then move it), or verify the caller ID again on the subaccount, or point the dialer at the account that actually owns the number.
Why does DialSheet show 21210 when the number is in my Twilio account?
Almost always because the credentials pasted into DialSheet belong to a different Twilio account or subaccount than the one that owns the number, or because the number was released or transferred after the caller-ID picker was last loaded. Open Settings, Twilio, and reconnect: DialSheet re-lists the numbers on the account those credentials reach, and the picker shows only numbers Twilio will accept as caller ID. If the number is missing from the list, it is on another account.
Does verifying a caller ID cost anything?
No. Verification is free and takes about a minute; Twilio calls or texts a six-digit code. A Twilio local number is ~$1.15/month plus usage. Neither changes what the call costs per minute.