Hi lavawater, can you give more information? Reading This Post and applying it's suggestions would help the tech team to help you resolve your situation more quickly. :)
I have one student copy the link and it worked but for the student it didn,t
Another option is for your student to go Here and submit the email thatyou are using for your Duolingo account. Please don't share your email with them via Duolingo, but rather, offsite.