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.
So far you should have understood the basics on how to use our products. This PDF, however, is what you need to make the most out of your order!