Jürgen, thanks for the quick reply! The website was previously installed
on another server. Lets Encrypt could not be installed there because the
webspace and domain had different addresses according to the company.
(See attached error message!) The company has now given us a new web
space and we have transferred the data there. Now we wanted to install
Lets Encrypt again via Plesk and it doesn’t work again! What could be
the cause? Maybe we made too many attempts to install Lets Encrypt on
the old webspace? I dont know! Jürgen, maybe you can help us and excuse
my bad english!
That's another ip address, that can't work using http validation -> configuration error of that domain name ws111468.mbmwebhost.net. That's the job of your hoster to fix that, it's their domain name.