Heishamon problems retrieving data with http get from PLC

[js-ed]

Good Morning
My heishamon (large version) works fine and I can download the JSON data with browser.
Sending commands and setting also works without any flaws using IP adress (192.x.x.x. ) or via DNS discovery (e.g. heishamon.mydomain.de) does not change anything.
However, when I try to do the same from a PLC with a HTTP Get command (Wago 880 using wagolibhttp_02 or ocsat GET_HTTP) a I always receive a timeout.
The same PLC Program can retrieve date form other sites ( JSON weather report from. openweather) without any problem
Looks like if I am trapped somewhere in a dead ending track.
Does anyone have an idea how to solve this problem ?
Thank you in advance
Jürgen