Citron Clown Goby

Beautiful fish. Arrived looking healthy and it was quite big as well. Only problem is after 3 weeks of trying multiple different foods it refuses to eat. Its looking pretty skinny already. Was very excited for this fish but have never experienced a fish not eating before. I've tried frozen mysis, brine shrimp flakes and pellets. Feel bad starving such a beautiful fish. Ive had a green clown goby that eats just fine so this is new to me the not eating.