Have you done a water check or a water change lately? If the toxins are high they'll get lethargic and stop eating. Try a 50% water change. How often do you do water changes and what % of water? Bullies, when eating, produce a lot of waste. Way more than we can see. Have you ever seen them pee? My 5" bully can pee about a 1/4 at a time. That's a lot if waste (ammonia). Doing partial water changes each week will help. A biological filter will help even more. Do you know if your filter has a bio filter pad in it?

Have you ever had fish tanks? Has anyone ever taught you about the nitrogen cycling in a live tank? If not, I can link some information for you.

If you can get a water test kit or strips this will give you more information as to if this is the problem or not.

How is the temp in there tank?

Force feeding is stressful, but may be necessary. Lets try a soak...

Pick up some plain, unflavored pedialyte and some reptaboost. Save the reptaboost for now. Give him a pedialyte bath. It's one part pedialyte to 10 parts dechlorinated water for 15 minutes. You can do the soak in a Critter keeper or tupperware with a lid with holes in it. Be sure to poke the holes in the lid from inside out so they are smooth so he doesn't get hurt. I very carefully use a awl or poker heated and I just poke holes right through the underside of the lid. If you do this, please be careful not to burn yourself. You can even set the container in his actual tank to help decrease stress, though you don't have to.

If he is toxic, soaks will help pull out some of the toxins. The pedialyte will help replace lost electrolytes.

Continue to offer food. Give him another day to see if he eats. Maybe he will feel better after the soak.

Let me know how he does. Lets hope he eats.