Getting an error when sending messages? This guide explains what each messaging error code means, why it happens, and how to fix it.
🏆 #1 Recommendation
Enable PhoneCheckr to lookup your contact phone numbers to ensure that you send to valid numbers that can receive SMS text messages.
By enabling PhoneCheckr it will help eliminate most errors when sending your texts.
Charge Denied
If you have the error charge denied, this is because your account ran out of credits and did not have enough credits to satisfy your broadcast. Once your credits go to 0, then Call Loop will stop sending your message.
Recommendation
🏆 Enable Auto-Recharge (recommended)
We recommend turning on Auto-Recharge, so when your credits fall below a certain amount, we will automatically add credits to your account.
2000 - 2999 Errors
21211
Invalid 'To' Phone Number
You attempted to initiate an outbound phone call, but the called phone number you supplied was not a valid phone number or was incorrectly formatted.
Possible Causes
The formatting of the 'To' number you supplied was invalid.
You attempted to send a message or place a call from a Call Loop number to itself.
Possible Solutions
🏆 Enable Auto-Recharge (recommended)
We recommend turning on Auto-Recharge, so when your credits fall below a certain amount, we will automatically add credits to your account.
21408
Permission to send an SMS has not been enabled for the region.
You have attempted to send an SMS to a region that has not been enabled in your account's. Call Loop is only available in the United States and Canada at this time.
Possible Causes
You have attempted to send an SMS to a region or country that is not available. Currently, Call Loop is only available in 🇺🇸 and 🇨🇦.
Possible Solutions
If you wish to send messages to a different country, please contact our support team for more information.
21606
The 'From' phone number provided is not a valid message-capable Call Loop phone number for this destination.
You can only send SMS messages from a phone number provided by Call Loop, and that phone number must be SMS enabled. You can only send SMS messages from a phone number or short code provided by or ported to Call Loop, and that phone number must be SMS-capable. For short codes, the From number must be in the same country as the To number.
Due to anti-spam regulations, the number a user sees when you send an SMS using your application must be the same Call Loop number associated with that account. This differs from voice calls, where it is possible to display a verified caller ID other than your Call Loop number.
Possible Causes
The Number you are using may not be capable of sending messages
The Number may be formatted incorrectly. Call Loop accepts numbers in E.164 format
If the Number is a short code, it must be associated with the same country as the destination address.
Possible Solutions
Check that you are using a Call Loop phone number with SMS capabilities.
If you are sending from a short code, verify that the country you are sending to matches the country of the short code.
21610
Attempt to send to unsubscribed recipient
The person you are trying to message has opted out of receiving messages from your Call Loop phone number. You have attempted to message a 'To' number that has replied with "STOP" to one of your previous messages.
Possible Causes
The end user handset has responded with "STOP" or another opt-out keyword.
Possible Solutions
Consider removing this phone number from your list of recipients.
Request the recipient to resubscribe to your messages by texting in "START" or another opt-in keyword to your Call Loop sender.
21612
Message cannot be sent with the current combination of "To" and/or "From" parameters
You have attempted to send to a number that is not currently reachable via Call Loop SMS. If the number provided is a properly formatted E.164, it is most likely that Call Loop does not yet have service with the carrier you are trying to reach. We have logged the carrier you are attempting to reach and will monitor these failures when adding new carriers. The combination of “To” and “From” parameters on this message cannot be connected by Call Loop at this time.
Possible Causes
Number formatting: The format you used for the “To” or “From” number may not be formatted using the E.164 format. Call Loop standardizes numbers using the E.164 format. If the “To” or “From” number of this message were altered by Call Loop in a way that you didn’t expect, try re-submitting the message with E.164 formatted addresses.
Possible Solutions
Check the format of your contact phone number to ensure the proper accepted format for the given country.
21614
'To' number is not a valid mobile number
You have attempted to send a SMS with a 'To' number that is not a valid mobile number. It is likely that the number that you have specified is a landline number or is an invalid number.
Possible Causes
The number you provided may be a landline number.
The number you provided may be invalid or formatted incorrectly.
If you are attempting to send SMS to Internet of Things (IoT) or machine-to-machine (M2M) numbers, the numbers may use a non-standard format that Twilio has not added to our number validation system yet.
Possible Solutions
Confirm that the number you are sending to is not a landline, using PhoneCheckr
Please verify you have provided a valid mobile number in proper.
3000 - 3999 Errors
30003
Unreachable destination handset
Possible Causes
Error code 30003 means your message failed to deliver because the destination was unavailable or unreachable. This error occurs if you are trying to reach an unreachable or switched-off destination handset.
This doesn't mean that it's a bad number, its simply that at the time of the message attempting to be delivered, it failed because the device was off or unreachable.
Most likely, the phone number is a LANDLINE and is unable to receive SMS
The destination number you are trying to reach is unknown or may not exist.
The device you are trying to reach is not on or does not have sufficient signal.
There is an issue with the mobile carrier.
Possible Solutions
The first step to troubleshooting this issue is to attempt to replicate the problems. Attempt to send another test message to this contact.
If you see similar results, continue troubleshooting with the following checklist:
🏆 Enable PhoneCheckr (recommended)
Enable PhoneCheckr to lookup your number to determine the number Type.
Send messages to only Valid numbers (type: mobile, voip) and skip sending to Landlines.
Is the destination device powered on?
Does the device have sufficient signal? If not power the device off, wait 30 seconds, and then power it back up.
Is the device connected to the home carrier's network? We cannot guarantee message delivery on devices roaming off-network.
Can the device receive non-Call Loop SMS?
Can the device receive messages from another Call Loop number (non-Alphanumeric Sender ID), or with a shorter one-segment (non-concatenated) body?
Can other devices using the same mobile carrier receive your messages?
30005
Message Delivery - Unknown destination handset
If a message you sent is not delivered to the end device and returns a 30005 error code, this means that delivery of your message failed due to an unknown or inactive destination number, for example, a number that is no longer in service.
Possible Causes
Most likely, the phone number is a LANDLINE and is unable to receive SMS
The destination number you are trying to reach is unknown and may no longer exist.
The device you are trying to reach is not on or does not have sufficient signal.
There is an issue with the mobile carrier.
Possible Solutions
🏆 Enable PhoneCheckr (recommended)
Enable PhoneCheckr to lookup your number to determine the number Type.
Send messages to only Valid numbers (type: mobile, voip) and skip sending to Landlines.
We recommend turning on Auto-Recharge, so when your credits fall below a certain amount, we will automatically add credits to your account.
30006
Landline or unreachable carrier
If a message you sent is not delivered to the end device and returns a 30006 error code, this means that delivery of your message failed due to the destination being a landline and incapable of receiving SMS, or an unreachable destination carrier.
Possible Causes
The destination number is unable to receive this message. Potential reasons could include trying to reach a landline or, in the case of short codes, an unreachable carrier.
Your message was sent to a landline, or an unreachable carrier for this phone number type.
Possible Solutions
🏆 Enable PhoneCheckr (recommended)
Enable PhoneCheckr to lookup your number to determine the number Type.
Send messages to only Valid numbers (type: mobile, voip) and skip sending to Landlines.
We recommend turning on Auto-Recharge, so when your credits fall below a certain amount, we will automatically add credits to your account.
30007
Message filtered
Your message content was flagged as going against carrier guidelines. Your message was filtered (blocked) by our vendor or by the carrier. This may be done by our SMS vendors or by a wireless carrier for violating carrier rules or regulations.
Examples of messaging that would be blocked by Call Loop are spam, phishing, and fraud. Call Loop's filtering system is in place to protect mobile subscribers from spam or other forms of malicious or unwanted messages.
Wireless carriers have filtering systems in place as well. These carrier filters are used to block abusive traffic, as well as to enforce rules or regulations about what types of messaging are allowed to that country or mobile network.
Possible Causes
Your message was identified as spam or unwanted messaging by our vendor's or Call Loop's message filtering system
Your message was flagged as objectionable and blocked by a wireless carrier
Possible Solutions
Local Phone Numbers
Register for 10DLC and get approved for your Brand and Use Case
Toll-Free Numbers
Other Recommendations
Ensure your messaging use case complies with Twilio's Messaging Policy and Acceptable Use Policy
Review the information in How Does Message Filtering Work? to understand what causes filtering.
See How do I prevent my Twilio messages from being filtered (blocked)? for specific tips on avoiding message filtering.
30008
Message Delivery - Unknown error
If a message you sent is not delivered to the end device and returns a 30008 error code, this means that delivery of your message failed for unknown reasons. When Call Loop receives a very generic error from our carrier partner that we have no further details about, we associate the message with the error code 30008, letting you know that Call Loop truly doesn’t know what caused this error from the provider.
Possible Causes
Check that the phone you were sending to is turned on and can receive non-Call Loop SMS
Ensure that the phone is not roaming off network. We cannot guarantee message delivery on roaming phones.
Try sending to other phones who have the same mobile carrier (you can use our Lookups API to determine the carrier if you’re unsure). If messages to other phones go through, the issue is likely device related. Try rebooting the device or contact the mobile carrier for help.
If you are sending SMS from an alphanumeric sender ID, see if using a Call Loop phone number works better. We’ve observed that certain networks may block alpha sender IDs.
If the recipient number is another Call Loop number, ensure that number has an action configured for its Messaging capabilities.
Try sending a shorter message to the phone, with simple content that does not include any special characters. This would give our support team an idea as to whether the failure is related to concatenation or character encoding.
Call Loop support can help investigate what went wrong with our carriers. Please open a support request and include a minimum of 3 or more message SIDs where a 30008 error was thrown. Per our carriers' requirements, these SIDs can be no older than 48 hours at most.
30032
Toll-Free Number Has Not Been Verified.
Toll-Free verification is required. You sent a message from a Toll-Free number to a mobile subscriber in USA or Canada. Call Loop requires all Toll-Free numbers to go through a verification process. The Toll-Free number you sent from has not been verified through the required verification process.
Possible Causes
Your toll-free number has not been Verified to allow sending of traffic in USA and Canada.
Your message content is being flagged as SPAM on an unverified Toll-Free number.
Your toll-free verification request was rejected.
Possible Solutions
Starting May 16, 2022, any newly purchase Toll-Free numbers on Call Loop will need to be verified or it may experience interruptions.
Review the Toll-Free Best Practices help article.
Error Code Categories
Message errors fall into four main groups:
1XXXX – Invalid Request Errors
2XXXX – Account-Level Errors
4XXXX – Delivery & Carrier Errors
10DLC-Specific Errors
1XXXX — Invalid Request Errors
These errors mean the message never left the carrier platform due to formatting or request issues.
10001 – Inactive phone number
The destination number is not active.
Fix: Confirm the number or contact the recipient’s carrier.
10002 – Invalid phone number
The phone number is not valid.
Fix: Validate the number format (+E.164 required).
10003 – Invalid URL
The URL is malformed or too long (max 2000 characters).
Fix: Shorten or correct the URL.
10004 – Missing required parameter
A required field (like to) is missing.
Fix: Review the error source and resend.
10005 – Resource not found
Incorrect endpoint or resource.
Fix: Verify the endpoint being used.
10006 – Invalid ID
Invalid resource ID or permission issue.
Fix: Confirm permissions and sender setup.
10007 – Unexpected error
Temporary system issue.
Fix: Retry and check system status.
10009 / 10010 – Authentication or authorization failed
API key missing, revoked, or lacks permissions.
Fix: Verify credentials and access level.
10011 – Too many requests
Rate limit exceeded.
Fix: Slow down sending speed.
10015 – Bad request
Improper request formatting.
Fix: Check message structure.
10016 – Phone number not in +E.164 format
Fix: Format numbers correctly (example: +15551234567).
2XXXX — Account-Level Errors
These indicate account configuration or funding issues.
20002 – API key revoked
Fix: Enable or regenerate your API key.
20006 – Expired access token
Fix: Refresh token or use current credentials.
20012 – Account inactive
Often caused by insufficient funds.
Fix: Add credits.
20013 – Account blocked
Fix: Contact support via online chat.
20014 / 20016 – Account not verified
Messaging requires account verification.
Fix: Complete verification steps.
20015 – Feature not enabled
SMS not activated on account.
Fix: Contact support.
20017 – Account not Level 2 verified
Required for alphanumeric sender IDs.
Fix: Complete Level 2 verification.
20100 – Insufficient funds
Fix: Add credits or enable Auto-Recharge.
4XXXX — Delivery & Carrier Errors
Messages were attempted but rejected by the carrier.
⚠️ Important:
Messages that leave the carrier network are charged, even if delivery fails.
40001 – Not routable
Landline or non-messaging number.
Fix: Validate numbers with PhoneCheckr.
40002 / 40003 – Blocked as spam (temporary / permanent)
Carrier flagged the message.
Fix: Review opt-ins, content, and sending behavior.
40004 – Rejected by destination carrier
Fix: Contact support if persistent.
40005 / 40006 – Message expired or server unavailable
Temporary carrier issue.
Fix: Retry later.
40008 – Undeliverable
Carrier rejected the message.
Fix: Validate number and content.
40009 – Invalid message body
Content violates carrier rules.
Fix: Review acceptable use guidelines.
40010 – Unregistered 10DLC message
Number not attached to a 10DLC campaign.
Fix: Complete 10DLC registration.
40011 – Rate limit exceeded
Sending too fast.
Fix: Reduce send rate.
40012 – Invalid destination number
Number is unowned, deactivated, or unreachable.
Fix: Validate with PhoneCheckr.
40013 – Invalid source number
Sender not properly provisioned.
Fix: Verify number setup.
40014 – Message expired in queue
Throughput exceeded.
Fix: Slow down sending.
40015 – Blocked as spam (internal)
Flagged by internal carrier filters.
Fix: Review use case and content.
40100 – Number not messaging enabled
Fix: Assign a messaging profile.
40150 – Toll-free number not registered
Fix: Complete toll-free registration.
40300 – Blocked due to STOP message
Recipient opted out.
Fix: Do not message unless they re-opt in.
40302 – Message too large
SMS segmented.
Fix: Shorten message or send MMS.
40305 – Invalid “from” address
Sender not approved or unhealthy.
Fix: Use a verified number.
40315 – Unhealthy sending number
Poor deliverability or high spam reports.
Fix: Rotate numbers or adjust content.
40329 – Toll-free number not yet verified
Verification pending or not submitted.
Fix: Submit toll-free use case.
10DLC-Specific Errors
40016 – T-Mobile 10DLC sending limit reached
Fix: Wait for daily reset or reduce volume.
40017 – AT&T spam rejection
Fix: Review content and opt-ins.
40018 – AT&T throughput limit reached
Fix: Reduce messages per minute.
Best Practices to Avoid Errors
✔ Validate numbers before sending
✔ Register 10DLC and toll-free numbers
✔ Send only to opted-in recipients
✔ Avoid spam-like language
✔ Control send rates
✔ Enable Auto-Recharge
Need Help?
Check the error code details above
Validate your numbers with PhoneCheckr
Contact our online chat for assistance
We’re happy to help you get messages delivered successfully 😊