Accessing a Web page by ip address fails, though success with domain name

I built a Universal Windows application that includes Web pages from a remote server (in the local network). Whenever I try to do so, it succeeds when I use a regular domain name as resource url, but I only get a blank page when I use the local ip address. I did add the ip address to the allowed domains, as I did with the regular domain name (e.g., I added www.google.com and 123.456.78.90), and I checked whether it was only for local network up addresses of fot all ip addresses, and the problem shows up with all ip addresses.

I'm quite stuck now, as I can only access the local server by ip, and I do need to include these pages from that server. Does anyone know this problem, and has some solution? Am I doing something wrong with the allowed domains? Am I missing some trivial setting?

Cheers, Dennis