Assign names to tasks via Slack

We started using Quire today and want to add tasks via Slack. This works but it gets problematic as soon as we assign a person to this task. Under https://quire.io/blog/p/Quire-and-Slack-work-great-together.html we found out how it should work. Can you explain which name of the team member we should put after the "@"? We've tried putting the name as it is in Quire or Slack and also the ID but neither of it worked. We always got the error notification "Sorry, we encountered an unexpected error. We will look into it, but feel free to contact us." Can you please look into it and explain how we can assign a team member to a task via Slack?