To me, it sounds like a respiratory infection and a vet visit is a must; however, I don't know if a vet could even help at this stage of decline. Is his mouth always open now? Or just some of the time? If his mouth is open only parts of the day, then I would say that he might have a fighting chance if you get him to a good vet. He won't be able to pull out of this on his own. However, it sounds like he is very close to the end. I'm super sorry that you have to deal with this. The breeder should have never sent a cham in this condition. Make sure to notify the breeder/supplier. Hopefully, they can give you a refund because this is ridiculous.
A respiratory infection (RI) makes breathing incredibly difficult. At first, they hide the symptoms for as long as possible. As the infection progresses, they point their nose up into the air to make the airway as straight as possible. The final stage is where their body shuts down; they close their eyes, open their mouths to increase airflow, and lose their strength to move. Your new addition seems to be in the final stages.
I'm not sure if he is even fixable at this stage. Even a vet will have trouble fixing him up. I think
@jannb will be able to help you find a reputable vet if that's the route you want to take. I agree with
@kinyonga, I'm not sure what more you can do to help him. If the vet does not have experience with chameleons, I would avoid them as they tend to do much more harm than good.
Once again, sorry that this happened to you. Let us know if you would like to purchase from a reputable breeder who will deliver a much healthier animal to you, we can set you up with someone.
I really think he is at death's door. I would keep him at an ambient temp near 74 degrees. Not too warm and not too cold. I would refrain from bothering him (i.e moving him back and forth from a basking spot).
I'm sorry that I cannot provide any more assistance, I have an extremely limited amount of experience. Hopefully,
@JacksJill or
@Kaizen can help.
Final thoughts: It's up to you to take him to the vet or not. I have no idea how much time he has left or even if a vet can help him. If he is completely unresponsive, I would leave him alone and let him die in peace. If he seems to be somewhat responsive, I would try taking him to an
experienced vet. Make sure to keep the supplier updated. This is ridiculous and you deserve a refund.