code: Observable<ComapiResult<String>> doCreateFbOptInState(@NonNull final String token) {
          return wrapObservable(service.createFbOptInState(AuthManager.addAuthPrefix(token), apiSpaceId, new Object()).map(mapToComapiResult()), log, "Creating fb opt in state.");
      }
docs: Gets the Facebook data-ref to create send to messenger button.
  
  @param token Comapi access token.
  @return @return Observable to get Facebook data-ref.