There is no SMS-gateway.apk application inside the archive.
I downloaded the Android application from here https://rbsoft.org/downloads/sms-gateway/sms-gateway.apk.
I installed the administrative part.
I installed the application on the phone.
Through the application on the phone, I enter the server, enter the name of the server + login + password.
I get an error: Invalid Purchase Code.
Isn't it NULLED?