Hi there, Alpha_T.
Thanks for stopping by the QuickBooks Community, At this time, there are some unaccepted characters within QuickBooks, these characters (including the Lambda) can cause server errors or other problems in the application. I'm providing a link to a list of acceptable characters, that applies to both QuickBooks Desktop and QuickBooks Online: Acceptable Characters.
If you have any other questions or concerns, feel free to post down below. Thank you for your time and have a nice weekend.