If you have a client that already uses thera-LINK with another provider, no problem! They will get an email that notifies them to accept your invitation. They just log in and accept your invitation under Settings>Practice. There will be a green check to accept the invite or a red X to reject.
Once joined, they'll be a member of both your practice and the other practice they were already a part of.
If you are a member of multiple practices (either in different or similar roles), you can switch between those practices using the drop down menu at the top. For instance, the below "pretend" client is a member of the following practices and can choose which one to see their appointments under or request an appointment from.