Sometimes if the doe isn't interested, the buck will do things to get her kind of agitated, which seems to be a way of getting her "in the mood." He'll try to chase her, but if the doe doesn't run away but just clamps herself down, the buck's attempts can include scratching at her, pulling chunks of fur, nipping around her head/neck/ears, etc.
It can take a while and a few exposures to the buck for the doe to become interested. One trick is to switch cages for her and the buck for a few hours/days, so she can get used to the buck's smell. I haven't found this to be especially effective, but some breeders I know use this approach all the time.
Other times when a doe isn't cooperative, some of us old-time breeders will put her in a carrier and drive her around for a while till she's hot and bothered. That will often do the trick.
Rabbits don't technically go into heat, and are induced ovulators (breeding behavior induces ovulation) but they do seem to have a 3-4 days "cycle" during which they're more receptive than otherwise. If she won't cooperate today, try again for the next few days. Between the normal cycle and the buck's attentions, you should be able to get her bred. Giving fresh greens can also spur some interest
