My bird didn't have AGY and no definitive diagnosis was ever made but she did have vomiting issues and would sometimes vomit the Reglan.
One thing that was recommended to me by the vet was providing her with ginger water. I would put some small strips of fresh ginger in
hot water and let that sit for a while, make sure it was cool and then add some of that to her drinking water. Ginger can be beneficial for
nausea and vomiting, but I would check with your vet first. She was also on vetri-DMG to help boost her immune system.
Sorry that your bird is ill and hope that he will get better soon.