custom shortcodes in newsletters

I am trying to make Mailpoet process a shortcode in newsletters, that works in posts or pages, by creating a custom shortcode following http://support.mailpoet.com/knowledgebase/hook-to-add-your-own-shortcode/.
The examples (my_name and blog_name) work fine, but the custom shortcode I made, that retrieves a list of the next 10 upcoming events from the Events Made Easy plugin, outputs the list to the upperleft of my browser window in a preview of the newsletter, instead of to the content of the newsletter.
Also if I send an example of the newsletter it pops up a message like “Request error Not JSON ….”.

Here’s the modified code I put in function.php:

/**
 * This is an example of a custom shortcode parser for MailPoet newsletters.
 * It's really easy to implement.
 * We already automatically parse all shortcodes with this notation for you: [custom:my_value]
 * You just have to add a filter and return the value you prefer.
 * In the following example we added [custom:my_name] and [custom:blog_name] to our newsletter.
 * We have now to return the preferred values, as string.
 */
// [custom:my_name]
// [custom:blog_name]
function mailpoet_shortcodes_custom_filter( $tag_value , $user_id) {

    // $tag_value contains the string after custom:
    // This function will be called the first time with $tag_value = my_name
    // The second time with $tag_value = blog_name

    // $user_id contains the corresponding MailPoet's subscriber id,
    // this could be useful to fetch extra data from the WordPress user's meta for instance
    // e.g.: https://gist.github.com/benheu/cf9eb925b0e17e6dbd6c

	if ($tag_value === 'my_name') {
        $replacement = 'Maily';
    }

    if ($tag_value === 'blog_name') {
        $replacement = get_bloginfo('name');
    }

   	if ($tag_value === 'eme_events') {
        		$replacement = eme_get_events_list('limit=10');
	}

    return $replacement;

}
add_filter('wysija_shortcodes', 'mailpoet_shortcodes_custom_filter',10 ,2);

`

Any help is most welcome…

Peter

https://wordpress.org/plugins/wysija-newsletters/