AFNetworking: success and failure blocks not called!! (POST to mysql backend) - objective-c

Question

I am still trying to get a hang of objective-c and AFNetworking. I am doing a POST (through UI button) on mysql backend which returns a json response. I can see the download progress, but my success and failure blocks are never called. Code snippet below. I only see 1 and 4 printed out.
NSMutableURLRequest *apiRequest = [self multipartFormRequestWithMethod:#"POST" path:kAPIPath parameters:params constructingBodyWithBlock:^(id <AFMultipartFormData>formData) {
NSLog(#"Success in calling");
}];
AFHTTPRequestOperation* operation = [[AFJSONRequestOperation alloc] initWithRequest: apiRequest];
NSLog(#"1");
[operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
//success!
NSLog(#"Response: %#", [[NSString alloc] initWithData:responseObject encoding:NSUTF8StringEncoding]);
NSLog(#"2");
completionBlock(responseObject);
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
//failure :(
NSLog(#"3");
completionBlock([NSDictionary dictionaryWithObject:[error localizedDescription] forKey:#"error"]);
}];
});
NSLog(#"4");
[operation start];
[operation setDownloadProgressBlock:^( NSUInteger bytesRead , long long totalBytesRead , long long totalBytesExpectedToRead )
{
NSLog(#"%lld of %lld", totalBytesRead, totalBytesExpectedToRead);
}
];