Hi,
To get what you want you’ll need to make the mashup setting “Post title and excerpt”. Then, enter the code you originally posted into the mashup-popup template:
<div class='mapp-title'>{{{post.title}}}</div>
<div class='mapp-body'>{{poi.props.projektadresse}}</div>I think I see the problem: when I pasted in your code, it contained curly quotes ( ’ ) instead of straight quotes ( ‘ ). Only straight quotes are allowed for HTML attributes. If you use the version above, it should work.
If that doesn’t help, please create the template as shown above and then *leave it active* so I can see it in the mashup (or send a login to the site for that purpose).