Hi Kia and welcome to BYC. I’ve suggested that you thread be moved to the Geese forum where you will get the best advice. I have no experience or advice to offer - sorry.
Kia how old is your goose and give us some back ground on it. what you feed where it lives. Could it have gotten into anything toxic? Symptoms I know you said he isn't eating anything else weak limber neck or wings?
If the goose's neck begins to be floppy, I'd venture it's limber neck (botulism). If you've had a lot of warm weather and migratory ducks/geese coming through, your goose may have been exposed to the botulism bacteria. They can be given a serum that helps the survival rate but it's not a sure thing. I'd keep him restrained in a run somewhere so he doesn't potentially infect your other geese. Read up on botulism treatment and see if it's something you want to pursue.