Brake caliper problem?

Am I missing something here? I can’t get the caliper to engage when bleeding and noticed the notches on the back of the pad but don’t see anything on the pistons, did I drop something and not notice?

Am I missing something here? I can’t get the caliper to engage when bleeding and noticed the notches on the back of the pad but don’t see anything on the pistons, did I drop something and not notice?