Implement a Get Request for RESTAPI

I can't connect with API using 'application/json' header on WebRequest command. Any advices?

string headers="application/json";

string res=WebRequest("GET",url,headers,timeout,data,result,result_headers);

Print("Status code: " , res, ", error: ", GetLastError());

Print("Server response: ", CharArrayToString(result));

Errors:

2020.03.28 19:26:01.978 2020.03.26 00:01:30  EA USDCAD,H1: Server response: add headers failed [87]

2020.03.28 19:26:01.978 2020.03.26 00:01:30  EA USDCAD,H1: Status code: -1, error: 5203