Send this reply:
Hi ____,
The student only needs the invitation link the first time they access the course. The first time they have accessed the course, it requires them to create an account using their username and password unless they already have an account.
To log back in to the course, go to https://canvas.instructure.com and enter your email address and password.
Please see these instructions: How to Login to Your CLEP or AP Prep Course
If this doesn't work or you would like a tech to call and walk you through these steps, reply to this message and request a phone call. Please include your phone number, time zone, and a good time to call that you will have access to the computer your student uses to access the course. Our tech team is available from 9AM - 5PM CST.
God bless you and have a great day!