Web Requests CRUD API Question

Hi. I am stuck on the following question:

“First, try to update any city’s name to be ‘flag’. Then, delete any city. Once done, search for a city named ‘flag’ to get the flag.”

I tried the following curl to "update any city’s name to be ‘flag’.
curl http://<SERVER_IP>:/api.php/city/London -X PUT -d ‘{“city_name”:“flag”}’ -H “Content-Type: application/json”

but I got an error: Unknown column ‘’ in 'field list. Any chance someone could help me out with the first part?