What is the api_site_parameter of stackapps.com in API 2.x? https://api.stackexchange.com/2.1/sites doesn't list stackapps. Why?
It's just stackapps, although you can also pass in the full domain stackapps.com.
The /sites route does indeed list StackApps, you just need to set an appropriately large page size (or page accordingly).
6 months ago