Doe might be not receptive, did he also stick his nose under her tail to smell her?
He tried, all the bits are there and look normal? Was the doe dominant (mounting him)?
Try again in about 3-5 days. Rabbits have a cycle, it may be the wrong time and that is why he quit.
Here if my bucks try they will get there provided doe is in fertile fase. One buck i kept from a litter that didn't do anything with doe in the pen (other than barely 2 seconds nose to nose and a ok, i have a roommate now) was cryptorchid and ended up in the freezer. Now i do observe closely the first 10-15 minutes or so, because a doe may mount the buck and scare him of trying anything or keep racing around till overheating/exhaustion. Neither is good for either of them. I may put a hand over the does eyes to keep her in place if she gets to crazy, but if she doesn't lift that is that.