Error prevents app_metadata update in Rule

[croptixsolutions]

I am unable to add app_metadata to a user using a Rule. I attempted to use the boilerplate code I found here in the docs:

Manage Metadata with Rules

function (user, context, callback) {
  user.app_metadata = user.app_metadata || {};
  // update the app_metadata that will be part of the response
  user.app_metadata.test = "test!";

  // persist the app_metadata update
  auth0.users.updateAppMetadata(user.user_id, user.app_metadata)
    .then(function(){
      callback(null, user, context);
    })
    .catch(function(err){
      callback(err);
    });
}

I receive the following error:

ERROR: The user does not exist.

What am I doing wrong here?

[croptixsolutions]

Update: This only seems to be an error when testing the rule. The rule does seem to work correctly when users authenticate.