rest api GET request wp-json/wp/v2/posts/id returns 403 error

Hello!

Any rest api url in the form of “/wp-json/wp/v2/posts/<id>” gives me a 403 on this one website.
Example: https://mysite.com/wp-json/wp/v2/posts/123

Several weeks ago the request was working.

All other rest api urls work fine, like for example:
https://mysite.com/wp-json/wp/v2/posts/

Even if I switch to twenty-fifteen and if I disable all plugins, the problem persists.

Do you know how I could solve this? Several weeks ago the request was working.

Thanks!