If I use my mobile Device via LTE i get the same message.
When I use my local PC, I am able to connect with the direct link(The IP Adress of my pi)
If I use the edge Browser from LAN and enter the external link,
I am rejected, or better not allowed to access
@devnull
It is solved.
Thanks for this hint.
I have seen, there was an underscore, automatically generated from the configtool.
I now removed it and I am able to access from the internet.