Vonage (Nexmo) for SMS Notifications

General Bytes offers the Nexmo (now Vonage) API to send SMS codes to your customers. The charges per SMS varies across regions. They typically run less than a single US cent per message.

NOTE: The major phone carriers around the globe impose limits upon the frequency of SMS transmission. They do this to prevent SMS spam & to provide a consistent service. The carriers use equipment that has limitations; there’s no getting around this. When these limits are exceeded, the carrier will “filter” out the excess SMS traffic, and those messages will simply be discarded: lost. You’ll commonly see these filtering events occur in batches.

GENERAL BYTES no longer offers Nexmo/Vonage (or Twilio) via the GB API.

  • You must signup for (and deploy in your CAS settings) your own Nexmo account.


Create your Nexmo account.

Free trial: https://ui.idp.vonage.com/ui/auth/registration

NOTE: the free trial will only work for testing the CAS API. This detail is not currently posted on their website or mentioned in their guides. You cannot use it for live SMS messaging (only for testing).

The The “free trial” number they provide may not work (for testing) for the first few days. Try sending a test from the Nexmo dashboard - if it works, then the CAS API test should also work.

You will have to add funds to:

  1. procure a toll-free number, or

  2. register a brand and campaign to send messages in the USA.

Either method will work, but each has it’s hurdles:

See: 10DLC (below)

An alternative for testing messages in the USA (that does not require immediate 10DLC registration) is purchasing and using a toll-free number (i.e., https://dashboard.nexmo.com/buy-numbers). However, the toll-free number will also get blocked after sending multiple messages in a short period of time. Eventually, a toll-free number also needs to be verified to prevent blockage.

  1. Enter your details, verify your access to SMS + email.

  2. No, not a developer.

  3. Role: Operations

  4. Select SMS

Due to new spam regulations imposed around the globe, carriers restrict SMS messages to “approved” use-cases. Vonage/Nexmo requires you to specify your use-case:


Cryptocurrency spam is forbidden:

  • do not use your Vonage account to send cryptocurrency ads or offers. Your Vonage account will be closed.

  • The use case of CAS is identity verification and notification (only).

    • Usage outside that case will likely trigger your account closure.


Locate and copy/save your API key and API secret:

Locate your working “from” phone number:


  • Copy the registered number you’ll use to represent you (the “from” number) in SMS messages.

  • The number must include the country code (“+1” in this example).

  • Scroll down to “SMS Provider”.

  • Select Nexmo.

  • Enter your credentials as a single-line string with no spaces: api_key:api_secret:from_phone


Example parameter string: 2f8a4afc:s3cr3t:+15555212855

Save the new settings!

Return and test.

  • If the green “successful” notification appears, then you’ve entered the parameters successfully.


The Vonage/Nexmo API won’t work with the “free trial” phone number. You’ll have to either procure a toll-free number, or setup your 10DLC campaign. The CAS tests may pass, but no messages will get through if Vonage/Nexmo has not approved your “from” number for the allowed/approved purposes.

If you abuse your privileges with the number given to you by Vonage, they may block your number. The SMS tests will pass (in CAS) but the messages will not get through.

Contact Vonage: https://api.support.vonage.com/hc/en-us/requests/new


10DLC is a type of long code number specifically designed for Application-to-Person (A2P) messaging. It allows businesses to send text messages to customers using a dedicated 10-digit phone number. The introduction of 10DLC compliance by major carriers in the United States aims to improve the overall messaging ecosystem, offering increased deliverability, reduced spam, and enhanced end-user security.

You must have a linked 10DLC campaign ID mapped to your +1 number when sending to the US. If you have not already completed 10DLC registration for your 10-digit numbers, please do so as soon as possible. 

10DLC related pages:

Critical pages to consider when sending campaigns for review:

Some guidelines to bring your campaigns to compliance:

  • Campaign Description - Detailed description of the campaign, such as an order reminder, shipment confirmation, hotel reservation, flight confirmation, etc., and if multiple types of messages, must list all

  • Sample MT Messages must indicate:

    • Brand name

    • Must have at least one example of each different type of message

  • Subscriber Opt-In Flow (aka Call to Action/Message Flow) - how the recipient learns about the campaign, and must indicate:

    • Brand name

    • Campaign description about how the recipient consents to receive messages

      • This is not required for one-time 2FA, but it should be made obvious that it’s one-time 2FA

    • Message frequency, such as "message frequency varies" or “recurring messages” (if campaign is recurring)

    • That ‘Message and Data rates may apply.’

    • Text HELP for help

    • Text STOP to cancel

    • Link to Privacy Policy

    • Link to SMS Terms and Conditions, which must indicate:

      • Required information includes: Brand Name, Program Description, Message Frequency disclosure, Pricing disclosure, Help Keyword, Stop Keyword, Carrier Disclaimer

  • Mobile Originated (MO) keywords HELP and STOP must be supported for all campaigns

  • Mobile Terminated (MT) Opt-Out and Help message responses are required for all campaign types - they are the messages that the recipient receives upon sending the STOP and HELP keywords

  • Opt-out sample message - response to STOP keyword - must indicate:

    • Brand name

    • Confirmation of opt-out 

    • and that the recipient will not receive further messages

  • Opt-in sample message is the first MT that the recipient receives upon subscribing to the campaign. One-time 2FA doesn’t require an opt-in sample message.  It is required for all recurring message campaigns that reach consumers on an ongoing basis.  Opt-in sample message must indicate:

    • Brand name

    • Message frequency (for ex. message frequency varies, recurring messages, #msgs/mo)

    • Opt-out information (Reply STOP to cancel) 

    • Customer care contact information (Reply HELP for help)

    • “Message and Data rates may apply” disclosure

  • Help sample message - response to HELP keyword - must indicate:

    • Brand name

    • How to receive help, that includes an email address, phone number and/or url that leads directly to a support contact page

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