For Pro-Coach accounts, inviting students works as follows:
1. go to "My students
2. click on the tab "Invite and connect students"
3. create an invitation link for each student and send it to your students.
Your students will open the link and register as students. (free of charge)
If the invitation was successful, you will see the students' names under "My students" and they will see you under "My coaches".
Then simply click on "Start Session" at the scheduled time.
(If the link does not reach the student, you can send a new one).