No access to open graph tags

We have a partner site which would like to show our content using our open graph tags, but apparently cant’t fetch topics when they enter one of our URLs.

I used https://opengraphcheck.com/ to check eg In der Schweiz wird eine riesige Batterie aus Beton gebaut - Magazin - 1E9 and it works fine, but when I use Open Graph Checker - Facebook Open Graph Tags Preview Online Free, I get the message “Invalid URL”.

For topics on https://meta.discourse.org/ it works in both cases. Any idea where to look for a fix? Thanks!