how to remove "Unable To Parse JSON Request" error?

hello,

getting an error "Unable To Parse JSON Request" while adding device id through mashup.

i have one code which gives me existing device id in database and i my another code is validation service created for the mashup where i wanted to compare device id present in database with the validation service input device id.

Now when i click on add band button it gives me an error "Unable To Parse JSON Request" i dont know why i am getting this error. below is my validation service code:-

// result: INFOTABLE dataShape: "checkBandDeviceDataDS"
let result1 = me.checkBandDeviceId({
device_id: device_id /* INTEGER */
});

if(device_id == "" || device_id == null){
result = 'Please enter device id';
}
else if(result1.device_id == device_id){
result = 'This device id is already exist';
}
else {
result = '';
}

above code is running perfectly when i run the personal code but it's not running through mashup, please suggest some solution on this, below is snapshot for your better understanding