Error: Server not found

It looks like your domain doesn’t point to your hosting space. What’s your website’s url?

As far as I can tell, you haven’t set up your domain name servers yet, so the domain points to nowhere – https://www.whatsmydns.net/#A/www.prochazkovapetra.cz

Where did you register the domain and where the hosting?

Yep, it seems that something somewhere wasn’t set properly by them (if they were supposed to do it). It is not about space, your newly bought domain doesn’t point to your hosting space. Contact their support and ask them to see what’s wrong.