KEYWORD_MISMATCH trying to add a number to an SMS phone pool

The error "KEYWORD_MISMATCH" occurs when you're trying to add a phone number to a phone pool, but the keywords configured for the new phone number don't match those of the existing phone numbers in the pool.

In AWS End User Messaging SMS, all phone numbers in a pool must share the same configuration, including keywords. As stated in the documentation, "The configuration of every phone number that you add to a pool has to match the configuration of the first phone number that you specified when you created the pool."

To fix this issue, you need to:

1. Check the keywords configured on your existing phone number in the pool
2. Ensure the new 10DLC number has exactly the same keywords configured
3. For each keyword, make sure the following elements match:

• The keyword text itself
• The keyword message (response message)
• The keyword action (AUTOMATIC_RESPONSE, OPT_OUT, or OPT_IN)

You can view and edit keywords for a phone number through the AWS End User Messaging SMS console by:

• Going to the Phone number page
• Selecting the phone number
• Navigating to the Keywords tab

Alternatively, you can use the AWS CLI to manage keywords using the put-keyword command to ensure both phone numbers have matching keyword configurations before adding the new number to the pool.
Sources
Add a keyword to a phone number in AWS End User Messaging SMS - AWS End User Messaging SMS
Edit a keyword used by a phone number in AWS End User Messaging SMS - AWS End User Messaging SMS
Phone pools in AWS End User Messaging SMS - AWS End User Messaging SMS