Hey!
I just used this with no issues: curl http://142.93.39.188:30592/api.php/city/London -X PUT -d '{"city_name":"flag"}' -H "Content-Type: application/json"
Reset the target machine and try one more time. If you get it to work, keep this thread in mind: Web requests - crud api
Feel free to DM me with screenshots.
-onthesauce