Download link with umlaut domains

Hi,

I use an umlaut domain (https://www.xn--iseler-mhle-0hb.de/, displayed in browsers as https://www.iseler-mühle.de).

In WP, permalinks is set to “post name”.

1. When I use the shortcode like this:
[download label=”Download Sample MP3 ?”]https://www.xn--iseler-mhle-0hb.de/wp-content/uploads/sample.mp3[/download]

the link is displayed as:
https://www.iseler-mühle.de/download/sample.mp3

and when I click on it, it cannot be found.

2. When I use the shortcode like this:
[download label=”Download Sample MP3 ?”]https://www.iseler-mühle.de/wp-content/uploads/sample.mp3[/download]

the link is displayed as:
https://www.iseler-mühle.de/download/https://www.iseler-m%C3%BChle.de/wp-content/uploads/sample.mp3

and this is completely wrong.

How do I have to set this up with an umlaut domain?

Thanks,
Stephen

https://www.ads-software.com/plugins/download-shortcode/