"The resource could not be found" when trying to get entries from sandbox environments

I can easily get all entries from my production (master) environment, it works fine. Problems start when I try to get entries from another environment (for example "development). I’ve got two sets of API keys, for production and development environments. As you can see on screenshots I’ve selected corresponding envs in API keys configuration menu. I do not get “The resource could not be found” error only if I use production API keys, i.e. when I make a request to production environment.

I can’t understand why such behavior appears. Shoudln’t it just show entries from the environment API key is linked to? Thanks in advance.

I’m using .NET SDK and I’ve got free account.

API keys configuration: