Have you enabled SMS sending for your extension? Under Users > you > General > SMS.The server is configured to do it.
How is it done in the Android app? I only see "Chat" with no option to type a mobile number (only 3CX extensions)
Is your DID set there? I don't see a DID in the list but not sure if you just redacted it.View attachment 31722
SIP trunk enabled for SMS
View attachment 31723
User enabled for SMS (but no option for configured trunk).
Founded in 2005, when VoIP was an emerging technology, 3CX has gone on to establish itself as a global leader in business communications.