Here you can see the script that will control the shelly device via MQTT with its topic configurations:

Topic Write

Topic: shellies/shellyswitch25-<deviceID>/roller/0/command/pos


Script: 

return payload*100.0;


Topic Event

Topic: shellies/shellyswitch25-<deviceID>/roller/0/command/pos


Script:

if(payload == -1){
    return 0;
}else{
    return payload/100.0;
}