Since two weeks I’m getting an error from “zypper -lu”:
Repository ‘openSUSE-Leap-42.3-Update-Non-Oss’ appears to be outdated. Consider using a different mirror or server.
It has worked perfectly before and I haven’t changed any repository, e.g. i have
http://download.opensuse.org/distribution/leap/42.3/repo/non-oss/
Do I have t change anything?
Thanks for a hint, rgds
Upgrade. 42.3 support has expired.
Leap 42.3 is end of life as of 31st June 2019 ( https://en.opensuse.org/Lifetime )
There will be no more updates available for that release … it’s time to upgrade 
…
The repository zypper is complaining about is not the same as the URL you post, which is the distribution URL. FWIW, I can (still) reach http://download.opensuse.org/update/leap/42.3/