A blocked crop or gizzard?
Generally when a crop has turned sour, it's due to yeast or it's fungal (think fermented feed, grass, etc.). Most of the time an anti-fungal is given instead of an antibiotic which could make a fungal/yeast infection worse.
Follow the instructions your Vet gave you, but I'd also do some reading/research to determine what may be the best course of treatment for Sour Crop. The way I treat is outlined in the article below.
Crop surgery is the last course of action to take if the crop is blocked with fibrous material that will not pass any other way, then it does have to be removed. IF it comes to crop surgery, then finding an Avian Vet that is well versed about Birds (poultry if possible) is a good idea.
https://www.backyardchickens.com/ar...w-to-know-which-one-youre-dealing-with.73607/