This error displays when inviting a collaborator to join a Padlet via 'Add By Email' in the Privacy menu.
If you have entered a Padlet username, 'Invalid User' may appear if the username is not registered on Padlet. Please note though that a sign up is not required to invite someone to post on your padlet. If you have an email address for the user you want to share Padlet with, you can add their email address and an email will be sent to them.
If you are entering an email address (registered or not) and see this error, please double check on the email address. There may be some errors (non alpha numeric characters) added.
Also, be informed that all email invitations are sent individually. (Nope, the comma trick doesn't work here yet) if you are adding a large volume of students to your private padlet, you can send student details to us and will be happy to add them for you! :D