Hi @FIMC-VI ,
Since you are using the free for teacher edition of canvas, I highly recommend directly reaching out to the canvas support team, as they would be the ones with the free for teacher administrative permissions to see what's going on.
Something else you could do is make your course public - (only available on k12, not canvas.instructure) - and select the option to add a join this course button. Then, send the student the course URL and have them join the course that way. That could be a solution, too. I've had to do that before.
Reach out with any questions, however I hope this gets you started!
Best of luck,
Noah