Command Fail

Hello,
I could connect to pi successfully and it says it is connected but when I run command "date" or "pwd" from android app, it does not works. I saw the result from console and could see the command seems is sent with wrong text.
[b'date']
[b'pwd'] 
And then py file code error which has exception issue on is_json function.
Can you please let me know what is the issue? 