Have  you checked if the json file is present in the test environment?

I think the most likely reason is, as Tomas suggests, that the file hasn't been deployed for some reason but, if the file is there and you're still getting a 404, it could be an issue with mime type mappings. If you're on .net 4.x, you can add a mapping for the file type in web.config like this:

<staticContent>
  <remove fileExtension=".json" />
  <mimeMap fileExtension=".json" mimeType="application/json" />
</staticContent>

If you're on .net >= 5, you'll need to add your mapping in your startup class using app.UseStaticFiles.