JSON Parsing Error Microsoft Emotion API ios - ios

Question

I am having problem in using the Microsoft Emotion API i have read the documentation but not able to use it. Whenever i use the below code it gives Bad body JSON parsing error. I am not able to detect whats the problem in code.
i have created a method
- (IBAction)clickToGenerateEmotion:(id)sender
NSString* path = #"https://api.projectoxford.ai/emotion/v1.0/recognize";
NSArray* array = #[
#"entities=true",
];
NSString* string = [array componentsJoinedByString:#"&"];
path = [path stringByAppendingFormat:#"?%#", string];
NSLog(#"%#", path);
UIImage *yourImage= _image;
NSData *imageData = UIImagePNGRepresentation(yourImage);
NSMutableURLRequest* _request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:path]];
[_request setHTTPMethod:#"POST"];
[_request setValue:#"application/json" forHTTPHeaderField:#"Content-Type"];
[_request setValue:#"9b118d1587ce40899598b48a6c29b51a" forHTTPHeaderField:#"Ocp-Apim-Subscription-Key"];
NSDictionary *params = #{#"\"url\"" : #"\"http://engineering.unl.edu/images/staff/Kayla_Person-small.jpg\""};
NSMutableArray *pairs = [[NSMutableArray alloc] initWithCapacity:0];
for (NSString *key in params) {
[pairs addObject:[NSString stringWithFormat:#"%#=%#", key, params[key]]];
}
NSString *requestParams = [pairs componentsJoinedByString:#"&"];
[_request setHTTPBody:imageData];
NSURLResponse *response = nil;
NSError *error = nil;
NSData* _connectionData = [NSURLConnection sendSynchronousRequest:_request returningResponse:&response error:&error];
NSLog(#"responseData = %#", [[NSString alloc] initWithData:_connectionData encoding:NSUTF8StringEncoding]);
if (nil != error)
{
NSLog(#"Error: %#", error);
}
else
{
NSError* error = nil;
NSMutableDictionary* json = nil;
NSString* dataString = [[NSString alloc] initWithData:_connectionData encoding:NSUTF8StringEncoding];
NSLog(#"%#", dataString);
if (nil != _connectionData)
{
json = [NSJSONSerialization JSONObjectWithData:_connectionData options:NSJSONReadingMutableContainers error:&error];
}
if (error || !json)
{
NSLog(#"Could not parse loaded json with error:%#", error);
}
NSLog(#"%#", json);
_connectionData = nil;
}
`
Thanks in advance!!!