You want to add a new user and you have entered the e-mail address, but now you receive the message that this user already exists?
In this case, you have the option of taking over the user data already stored. Use the drop-down menu to select the role you want this user to play in your organisation and then click on the button "Add existing user".
You will find an explanation of the respective roles in the dropdown "Security & Permissions" in the "Role" tab.
The user will now be added to your organisation (click on the cogwheel next to your profile).
In addition, the user's profile will show the new organisation to which he or she has been added.
Further information on the topic User Account & Organisations