Wordpress JSON API returns normal site page in html. How do I get it to give me JSON like it's supposed to

[admin]

For example, entering

http://mywordpresswebsite.example.com/?json=1

into the browser loads the main site html, the same as omitting the json querystring variable:

http://mywordpresswebsite.example.com/

The JSON API is activated. I have tried reactivating and deactivating, checking .htaccess file settings, and deactivating all other plugins. None of those have made much difference so far.

TIA