how long has he not been eating? Has he been weaned off live foods yet, and then stopped eating? If you are just starting to try to get him off live foods get some squid either from you grocery store or lfs, and cut it into strips 2"-3" long, then take a piece of rigid air tubing and put the squid on it then wiggle it in the water so hat it looks alive, move it away from the lion as he comes to investigate, usually they will eat it. I like to use either squid or clam for this because it stays on the air tube better. eventually your lion will eat whatever you offer without the air tube. If his refusing to eat continues you may have to feed a few live ghost shrimp to keep him strong. Just be patient, lions can go a long time without eating, sometimes a week or two.
Good luck