good afternoon!
The problem most likely lies in the Cisco ISE sms gateway.
The operator for sending SMS is Megafon. He sent the HTTP Post settings. the documentation describes a secure HTTPS connection, and the authorization method on the operator's server is Authorization Basic.
We reviewed the sent packets with the built-in TCPDump program. it shows that the login-password data "Authorization Basic" is not created by the Cisco ISE system. authorization does not take place on the server side. This is confirmed by the telecom operator.
Please help me solve this problem.
Below are screenshots of the SMS Gateway settings and the operator's instructions.