Dart - Why do I have to await this either.fold call

Question

    Future<Either<Failure, User>> call(SignUpParams params) async {

    Either<Failure, User> failureOrUser;

    // Creates a User
    failureOrUser = await repository.signUpUser(
        params.email, params.password, params.type);

    // Creates a [Learner / Instructor] if User returned
    await failureOrUser.fold(
            (failure) => left(failure),
            (user) async {
              final remoteServerFailureOrSuccess =
                await createLearnerOrInstructor(CreateLOIParam(user: user));

              // check if [Learner / Instructor] creation has failed
              remoteServerFailureOrSuccess.fold(
                      (failure) => failureOrUser = left(failure),
                      (success) => null
              );

            }
    );

    return failureOrUser;
} 

I cant figure out why I need to place an await in front of failureOrUser.fold(); method.

If I dont then the (user) async {} method doesnt await

final remoteServerFailureOrSuccess = await createLearnerOrInstructor(CreateLOIParam(user: user));

and return failureOrUser; is called before

remoteServerFailureOrSuccess.fold(
  (failure) => failureOrUser = left(failure),
  (success) => null
);

is called.

Im getting an 'await is applied before 'Object', which is not a Future' error tip but the code only waits till the whole method is finished before returning, done this way.

Ive tried putting

await remoteServerFailureOrSuccess.fold(
 (failure) => failureOrUser = left(failure),
 (success) => null
);

but this still doesn't work.

So to me it seems like

final remoteServerFailureOrSuccess = await createLearnerOrInstructor(CreateLOIParam(user: user));

isn't actually awaiting.

Solution

Okay I think I figured it out, because I set (user) async {} it made the fold a Future, but the other half wasn't async (failure) => left(failure) so i assume i was getting the error because of that.

Once i set the failure to be async the error went away. (failure) async => left(failure)

Bit of a silly question but i'll leave it up incase anyone gets the same error.