Hello @adcadesigns
You can’t add a shortcode but you can add your own short tag to be used in the email template as explained in this article.
Here is an example of how you can use shortcode with custom short tag:
add_filter( 'um_template_tags_patterns_hook',function($search){
$search[] = '{say_hello}';
return $search;
}, 10, 1 );
add_filter( 'um_template_tags_replaces_hook', function($replace){
$replace[] = do_shortcode('[say_hello]');
return $replace;
}, 10, 1 );
add_shortcode('say_hello',function(){
return 'Hello There!!';
});
With the above code example, you can include {say_hello} on your email template and that will be replaced with “Hello there!!”
I hope this helps.