They often go for bloodworms. Frozen may work. Or chopped shrimp. Sometimes they eat at night, so you might not see it eat. Some will go awhile without eating. Some need live fish to eat, as they want to hunt. Small fish, white clouds, guppies, etc.
But bloodworms should get some reaction,most carnivores love them.
Bit of chopped beef heart, might be ok. But I would not feed ordinary meat to a fish.