meta_query not working with the_content()

the_content() echoes data to the page so essentially your query looks like:

'meta_query' => array(
    array(
        'key'     => '',
        'value'   => $related_venue_variable,
        'compare' => '=='
     )
)

You want get_the_content() to return a string that you can pass along through the query.

However, having the post content as a meta key doesn’t make any sense. For one, that key only holds 225 characters. Given that you may be storing the key from another post in the post content of a second post, that may not be a problem, but any filters applied on the post content will be as those can alter the content retrieved. In short, what you are doing is a bad, bad idea.

Now I’m guessing, but I think this is close to what you want to achieve:

if( have_posts() ) {
    while( have_posts() ) {
        the_post();

        $args_up = array(
            'post_type'         => 'events', 
            'posts_per_page'    => 20,
            'paged'             => $paged, 
            'meta_query'        => array(
                array(
                    'key'       => $post->post_content,
                    'value'     => $related_venue_variable,
                    'compare'   => '=='
                )
            )
        );

        $eq = new WP_Query( $args_up );
    }
}

But it’s still a bad idea to save a key as post content. You’d be better off saving it as custom meta in both posts. Of course, there might be a better way to do this all around if I knew exactly how it all went together.

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