Ikea Pax sliding door scrapes and makes noises

Hello! Over the weekend we assembled a Pax wardrobe (2 x 100 cm). The sliding doors (at first only the back one) move very stiffly and squeak. What did we do wrong???????? :eek:

Thanks for your help

Gina

The door is hung too low at the bottom, that is, not in the rail but behind it.