Two last basics
Twisted strap & wrong thumb position - the main 2 mistakes our clients make!
Before doing the loop with the strap, already hold the handle in a position you want to use later! In this way the strap will stay aligned / not twisted, which leads to no pressure on your fingers while lifting.
Another issue that can cause this (mostly by using heavy weights): Putting your thumb below the handle, not above or on the side instead. This could cause problems since the handle will not be aligned straight/ might be inclined so the fingers will be pushed towards the strap.