Using Sendbird with FlutterFlow

Has anybody managed to use Sendbird with flutterflow.io? I’m trying to set up a quick proof of concept for an app but I’m struggling to get flutterflow to accept custom code to connect to sendbird. I can’t find any tutorials on it anywhere. Specific problem (currently) is that it won’t save a custom action because it can’t process the return parameter (User). Many thanks to anyone who can help!