Vertically angled runners
The majority of all runners (that connect your curtains to your curtain track) are vertically straight. However, a small number of systems come with runners that have a vertical angle. The Slide Mounting system only works with runners that are vertically straight or have an angle of no more than 30 degrees.
If you have runners that are vertically strongly angled ("bent"), then you will either need to straighten or replace them.