Hi and welcome. Looks like you’ve gotten some great advice already.

Bless you for caring for this poor little guy. For all that you are doing for him, you really should keep him. I am not a vet and have not personally dealt with a situation such as what your chameleon is in, but I will do my best to offer some help.
Although the enclosure he’s currently in is too small for an adult, it is actually ideal while he is sick and recovering. Aside from the correct uvb light (will return to this in a bit), you really need to find some phosphorus free calcium without D3. That needs to be lightly dusted on his insects for every feeding. Using the Repashy calcium plus LoD one feeding every two weeks is perfect. This supplement regimen is for a healthy chameleon. A few years ago, it was thought and said that the Repashy calcium plus LoD could be used for every feeding and many of us tried that. My veiled girl and many other’s chameleons developed edema and my vet advised to use once every two weeks. Some chameleons have tolerated it being used at every feeding, but those usually are panthers and I’m not aware of their full husbandry. Very often the symptoms of too much vitamin D3 are similar to MBD. I would hold the LoD for a couple of weeks and just give the plain calcium. Taking him outside for some natural Vitamin D may also help lower the levels of supplemental D3, but I‘m afraid I don’t recall how that works. There is also preformed vitamin A in the LoD, which is probably also contributing to all.
I’m sorry that your postal delivery is lacking. Perhaps you can find in a local pet store a correct uvb light. While the current standard is a T5HO fixture with either a 5.0 or 6% uvb bulb, you could also use a T8 with a 10.0 or 12% uvb bulb, which is older type. Then you can have basking area about 17-22cm below. For basking temp, since you have a pre-adult male, your current temps are just a little bit high. You can have a temp as high as 29c. Do make sure to provide some shaded and cooler areas so he can have some choice. Using live plants will help with that. Pothos is the most common and perhaps the best plant for chameleons. Another that is one of my favorites is schefflera. Make sure the leaves are clean from any chemicals - usually a wash of the leaves with gentle dish soap and a thorough rinse helps. For hydration, you want to mist the plants for about 2 minutes, twice a day - right before lights go on and off. If needed, you could use a dripper for 15-20 minutes too. Very easy to make your own - use a plastic cup or bottle with a pin hole on the bottom. Giving the ReptaBoost is fine and no real need to add insects to it. Like 3 days ago I came across the notes I took that had the ideal amount of ReptaBoost to give one of my chameleons when he was failing…and I tossed it out.

There are instructions which include how much to feed. It took me a minute to figure it all out - so if you need help with that, just ask. I always gave a little bit of water after too…usually about 0.5 ml or so. I tried not too give too much orally at one time to help with tolerance. I’m not sure about intraperitoneal fluids. I would think it safer to give subcutaneously instead. Since you are a veterinary student, I don’t think I have to tell you, (but I will anyhow) that the airway is in the front of the mouth, so aim for the back of the throat.
The ideal daytime humidity for a veiled chameleon is between 30-50%. If you are having a problem keeping it that low, do make sure to have excellent air flow and preferably a screen enclosure. High heat plus high humidity is a recipe for respiratory infection. At night, if you can achieve temps below at least 20-21c, you can use a fogger or cool mist humidifier and raise humidity all the way up. That simulates the hydration obtained in the wild thru night time fog.
I’m probably repeating much of what has already been said.
@kinyonga or
@jannb know so very much more than I do and may have some better advice.
I’m very glad that you found your way here.
