Include is usually used for including another Web Template (but believe it can be used for Content Snippets also using the correct format), for a Content Snippet you should be able to one of the following
{{ snippets["<<snippet name>>"] }}
or
note: replace only the <<snippet name>> in the below the first snippet_name is a keyword
{% include 'snippet' snippet_name:'<<snippet name>>' %}
I have never used the Include but do use the snippets one.
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