Problem with rendering and glass preview?

Question

3D

I did everything as in the video: https://www.youtube.com/watch?v=LFwopVJjRUo

A transparent strip appears on the mug, I started my hobby only 2 days ago, so I didn’t really find an answer, or I didn’t drive in the essence of the problem correctly. I attached the material settings and the problem itself below

(Render in cycles)

Answer 1

If there are no other materials on the object, then you need to check the normals on the object.