Sorry to hear. I’ve never had to deal with that before. If you’re sure it’s sour crop then you’re dealing with a yeast infection in the crop. There are some OTC yeast meds people use on their chickens that are meant for fish. I wanna say ketoconazole, but you should research it. Do you have any vets nearby that will treat chickens? We have Weare/Hopkinton animal hospital, but it gets pricey and I’m usually left feeling underwhelmed when I leave.