Webview in Sitemap says "Webserver XXX hat die Verbindung abgelehnt" (connection refused)

Hi together,

one more time, where I don’t know where the problem is located.

Lets start at the beginning:
I have installed a Webserver on my QNAP NAS which works fine. That means, that I can connect to it as well as can call a php file which displays me a table with entries from a mysql table from any browser from any local machine.

Then I tried a webview within my sitemap with a link to the php file as described above. It is curious, because if I call the sitemap from a browser, the webview only displays a error message, that the connection was refused by my webserver host. But if I call the sitemap with the webview from my android openhab app, it displays the tables as expected.

Do you have an idea where the problem is located?

Thx a lot!