Maybe try a mouse or smaller rat. My brb would act similar when I was offering medium rats, he refused them often. Then one day I offered a small rat and he hammered it. Now he eats a couple each feeding. I dont know what it is but he eats smalls so that is what he gets. The medium were not to large as he is 6ft and around 1900 grams but he only rarely ate them. Some snakes are just strange.

That or try live