"Security Requests from Sender" Pop-up notification message ?

Hello ​@Mike Beveridge

Thank you for reaching out, and welcome to the Docusign Community! I can see how frustrating this must be especially after you’ve already tested different scenarios and the explanation doesn’t fully match what you’re experiencing. It makes sense that you’d expect consistent validation behavior, and I understand why this situation feels unclear and difficult to troubleshoot. In Docusign eSignature, the system does enforce basic format validation based on country code (as you mentioned). Still, it typically does not validate whether a mobile number is truly active or reachable. That’s why “invalid” numbers can still pass initial checks and allow the envelope to be sent.
In cases like the warning/notification you’re seeing, it’s often related to one of the following scenarios:

• The number passes format validation but fails downstream delivery checks (e.g., carrier rejection, unreachable number, or SMS delivery limitations)
• The number may be technically valid in structure but not provisioned for SMS
• There could be carrier or regional restrictions affecting delivery
• Temporary issues such as SMS gateway delays or failures

To better check this, you should reach out to support. Since you mentioned you already asked support about this issue, please share the support case number via private message so I can check and follow up with them. 

For more information, here’s a related article you can check.
Send an Envelope by Email or Text Message (SMS)

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Sincerely,

Ma. Cassandra | Docusign Community Moderator
If this helped, feel free to Like👍and click "Best Answer."

Hello  ​@Mike Beveridge 

I trust all is well. We’d like to know if the suggested solution was helpful. If yes, we would greatly appreciate it if you could mark it as "Best Answer" ✅, to help other community members find trusted answers.😊
 

Let us know if you need further assistance—we're here for you!

Sincerely,

Ma. Cassandra| Docusign Community Moderator