How often are you trying to feed him? It adds stress to offer too frequently, so don't try to feed him more than once a week. You might even want to ignore
him for 2 weeks, just to see if that perks up his interest.

Are you trying to feed in the evening/night-time? Is he in his hide, & peeking out when you offer? (that's usually best, they like to ambush prey) If a BP is
cruising the cage they won't usually want food, because they feel too exposed...they feel safer to grab prey when in their hide.

After offering him the prey, have you tried just leaving it over-night, lights out & without hovering (watching) him? Some snakes prefer that privacy.

You might want to try a different prey: if you're feeding him mice, try a rat-fuzzy. What size prey have you been offering him? Now & then it turns out the
wrong size food is being offered, & that can also matter; his prey should be roughly equal to the size of his unfed-midbody.