You have received this error because the teacher you are trying to invite has not yet registered with TeachKloud. To successfully invite a teacher to use TeachKloud:
1. The teacher should go to https://dashboard.teachkloud.com/register and create an account using their primary email.
2. When they have done so, on the left-hand side of your TeachKloud dashboard, under the header "settings" select "teachers."
3. On the top right-hand side of your screen, enter the same email the teacher used to sign up to invite them. The teacher will receive a confirmation email.
Please ensure you use the same email address your teacher used to create their account to invite them.