Just want to verify that you got that Zilla T8 UVB tube strapped to the underside of the mesh lid, so that there is absolutely nothing between the tube and him, and that his basking spot/platform is at least within 6" of the now unobstructed UVb tube? That UVB tube is very weak, and if he is not able to bask within at least 6" of the tube then he's not getting adequate UVB or UVA light, and he won't have an appetite. Your tank looks quite tall from the photos, so if the tank is 12" tall or taller and you have the entire fixture strapped to the inside of the tank, then it's still almost 12" away from the floor of the tank. I saw how low you have his hammock to the floor, so I'm wondering if that's his "Basking Spot", or do you have something that is higher (and preferably solid instead of the mesh) on the Hot Side of the tank that is within at least 6" or closer to that UVB tube? If not, then that's your problem, and if you didn't get it under the mesh (I couldn't find anywhere you said that you strapped the entire UVB tube fixture under the mesh lid, so I'm just making sure, as this is crucial) then that's really the problem. You can only leave the much stronger T5 UVB tubes on top of mesh lids, as they are the only tubes strong enough to still get adequate
UVb light to your dragon on the other side of the mesh.
Just another FYI about that T8 strength UVB tube made by Zilla: In addition to having to be strapped underneath the mesh lid, and having to be within at least 6" of your dragon on his basking spot, and also having to be on for at least 13-14 hours every single day (along with his bright white colored Basking Bulb), it also must be replaced every 6 months at the very latest. The T8 UVB tubes have a very fast UVb decay rate, and at 6 months old they no longer emit adequate or any
UVB light.
When that Zilla Desert 50 T8 UVB tube is 6 months old and needs replaced, I highly suggest that you either upgrade to the 18" Reptisun 10.0 T8 UVB tube, which you can put into the Zilla Slimline fixture you already have (the Reptisun 10.0 T8 UVB tube will still have to be mounted underneath the mesh lid, be within 6" of the basking spot, and be replaced every 6 months, however it's a much higher quality UVB tube and does not emit any harmful light rays as a byproduct of the manufacturing process, as the Zilla, All Living Things, Reptile One, and many other brands do), OR better yet, you spend around $55 on Amazon.com and you upgrade to a 22" Reptisun 10.0 T5HO UVB tube and a 24" T5-rated tube fixture for it. You can buy both for around $55 shipped on Amazon.com, and the T5 UVB tube can sit on top of the mesh, it only has to be within 11" of his basking spot, and they only need replaced once every year. So it's a much stronger UVb and UVA light for your dragon, and it also saves you money because you only have to replace it once a year instead of every 6 months.