This is my first go a skeletons and animation and i'm stuck/

I'm trying to make a walk cycle and i have trouble animating it. I've made the legs and added the IK Handle's. I animated the leg moving up & forward but bringing the step down & forward is where i'm stuck as the leg wont go down that far as there is a bend and the knee.

I think there may be a problem with the arrangemant in the hypergraph.

Can anyone tell me what i'm doing wrong and/or direct me to a tutorial.

And, so you can see the problem 1st hand, here's the file.