Have you tried adding garlic? that combined with mixing live brine with frozen Got my Citron Clown goby(yellow with neon stripes) eating and established, he's as fat as can be now, though he still spits out food sometimes i think its just part of their eating habits.
I've seen alot of clown gobys with the feeding issue. I had 3 Citron clowns who never Ate and ended up perishing. I heard its quite common and has something to do with alot of them being caught with cyanide. I ended up getting a pair from Nuxx on here back when he ran Coral Imports and those were the only two i ever got to eat.
In my opinion and experience the hardest part of dealing with clown gobys is getting them eating. Once established they're pretty darn hardy.