There‘s probably ice between the binding and the ski. Bent the ski hard with your hands several times to break the ice.

There is snow or ice under the baseplate. Adjust your climbing aid in a higher position.

There is snow or ice under the heelplate. Put your ski into a vertical position. Bent the base plate several times with your hand to loosen the snow.

Put your Ski in a vertical position. Then clap the binding and skit together to knock off excess snow. Press the binding to the ski with your knee an secure the lever. (also see video "Introducing Marker Tour F10 & F12" on Marker youtube channel)

Most likely there is ice between the binding and the ski. Bent the ski several times hard with your hands to break the ice.

The BC lever wasn‘t fully laid down. When locking the binding take care that the rubber band doesn‘t get caught between lever and ski.