Welcome to the Forums, Parrot kid and your baby Sun.
Do you have experience with raising baby parrots and hand-feeding? I'm very sorry to say that it seems that your sun conure was too young to have been sold to you. Not your fault as it is unfortunately quite common, but it really should not be permitted for various health and ethical reasons, and sadly there is a lot that can go badly wrong, even for those with lots of experience with hand-raising very young birds. The really should not be sold until they have been eating solid adult food independently for at least two weeks.
I am not a bird breeder myself, but we have a wonderful member who is, and I have linked up one of his posts here, in the hope that it might be of some assistance to you...
And another resource written by a very experienced member here that may have some info that will help you...
Today I spent several hours trying to help someone save a baby bird they had purchased unweaned. The baby died; they are usually almost dead by the time the new owner realizes something is wrong, not because the owner doesn't care but because they are not educated about what to look for or...
www.parrotforums.com
Personally I would be seeking support and advice from a certified avian vet if you have access to one at a critical time like this. I'm not sure where you are located exactly but hopefully the link below may assist you in finding one close to you...
If there is not an avian vet anywhere close, I hope you can continue to approach the breeder you got him from for support with hand feeding and weaning onto adult food.
Thank you for joining and for reaching out for help, and I wish you and your baby Sun all the very best!