AFNetworking HTTP POST Success Empty - ios

Question

I need to make HTTP POST request, in that request I have to send some text fields and couple of files.
Every time I make the request, the files are uploaded, but I get such response.
"Success: <656d7074 79>" (aka "empty")
Here is the code, my parameter dictionaries are .
AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
manager.responseSerializer = [AFHTTPResponseSerializer serializer];
manager.requestSerializer = [AFHTTPRequestSerializer serializer];
AFHTTPRequestOperation *operation = [manager POST:url parameters:nil constructingBodyWithBlock:^(id<AFMultipartFormData> formData) {
// Append Files
NSError *error;
for (NSString *filePathsKey in filesPathsDictionary) {
[formData appendPartWithFileURL:[NSURL fileURLWithPath:filesPathsDictionary[filePathsKey]] name:filePathsKey error:&error];
if (error) {
NSLog(#"%#", error);
}
}
// Text parameters
for (NSString *textParameterKey in textParamDictionary) {
[formData appendPartWithFormData:[textParamDictionary[textParameterKey] dataUsingEncoding:NSUTF8StringEncoding] name:textParameterKey];
}
} success:^(AFHTTPRequestOperation *operation, id responseObject) {
NSLog(#"Success: %#", responseObject);
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
NSLog(#"Error: %#", error);
}];
[operation start];
UPDATE:
Changed my response serializer to JSON, because I'm expecting JSON
manager.responseSerializer = [AFJSONResponseSerializer serializer];
manager.responseSerializer.acceptableContentTypes = [manager.responseSerializer.acceptableContentTypes setByAddingObject:#"text/html"];
And getting this error:
Error: Error Domain=NSCocoaErrorDomain Code=3840 "JSON text did not start with array or object and option to allow fragments not set." UserInfo={NSDebugDescription=JSON text did not start with array or object and option to allow fragments not set.}