1.) Are you on a trial version or paid version of Teams (I.e. within Office 365) 2.) Where did you create the Team? In the Teams client, Web client, Teams Admin Centre? 3.) Are the member you are adding part of your organisation, or are they a guest? Do they have a Teams licence? 4.) What is the error message when trying to add? 5.) Does this happen to a particular member? Or when trying to add anyone within the organisation as a member? 6.) Did this just start or has it always been the case? 7.) Are you a member or the owner of the Team at this point?