Symptom
/wp-json/wp/v2/plugins/{slug}%2F{file} returns 404. Plugin activate / deactivate is blocked.
Cause
Apache rejects encoded slashes.
Workaround
POST https://example.org/index.php?rest_route=/wp/v2/plugins/wordpress-seo/wp-seo
body: {"status":"active"}The rest_route query form works (200).
Stepped on alongside: don't judge from active plugins only
Concluded "there's no SEO plugin." It was installed and inactive. GET /wp-json/wp/v2/plugins lists everything including inactive; use that.