No rich snippets / no structured data

(Sorry if the answer to whis question is too simple.)

I installed the plugin and placed just the shortcode to a page. Users who visit it can see the stars and rate.

But the plugin did not add any JSON-LD to the source-code of the website.
So there are no rich snippets and no structured data. I tested with the google tools.

Is there anything to add manually? (html, php?)
What did I wrong?

[rich snippets are enabled… content: “@context”: “https://schema.org/”,….]

Would be thankful for any help.

Version 4.1.3