安卓能够正常访问接口，iOS报500错误，原因是AFNetworing写了
[manager.requestSerializer setValue:@"application/json" forHTTPHeaderField:@"Content-Type"];
AFHTTPRequestOperationManager * manager = [AFHTTPRequestOperationManager manager];
manager.requestSerializer = [AFHTTPRequestSerializer serializer];
[manager.requestSerializer setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
NSDictionary * dict = @{@"key":value};
[manager POST:url parameters:dict success:^(AFHTTPRequestOperation * _Nonnull operation, id _Nonnull responseObject) {
} failure:^(AFHTTPRequestOperation * _Nonnull operation, NSError * _Nonnull error) {
}];
