Attempting to renew cert (www.whyyte-invest.de) from /etc/letsencrypt/renewal/www.whyyte-invest.de.conf produced an unexpected error: Failed authorization procedure. www.whyyte-invest.de (http-01): urn:ietf:params:acme:error:unauthorized :: The client lacks sufficient authorization :: Invalid response from http://www.whyyte-invest.de/.well-known/acme-challenge/RTrAugRTZp4Pf4YOXI3IgfzPm0m_g8v8-SEOQ_BYLpE [185.244.195.184]: 503. Skipping.
All renewal attempts failed. The following certs could not be renewed:
/etc/letsencrypt/live/www.whyyte-invest.de/fullchain.pem (failure)
Your site needs to be online for the authentication to succeed. Or at least it needs to successfully have access to the webroot without any automated error messages.
Just a minute ago, your site responded with “offline.” to any request, including the authentication token in the link in your post. Now, your site is completely down, no response on port 80 nor 443.
As of yet, your site still responds with "offline." for every request I make, including the authentication token.
As long as your site is responding with a general error message and not serving files from the webroot, renewal won't work.
You'll need to "fix" your nginx not to return a HTTP 503 Service Unavailable error message with offline. as contents. It should at least respond with a HTTP 200 OK (the normal response) with the contents of the file requested when requested a file from /.well-known/acme-challenge/.
But WHAT did you try? And why EXACTLY didn't it work? (I.e., what was the expected result and what did you get?) And most importantly, what were you trying to fix? Certificate renewal? Or your nginx server/website in general?
You're telling us two things here, which aren't really making any sense. You SAY you "open the site", but the error message you're telling us here is from certbot, the ACME client used for certificates. Those two things are totally different, opening a site and running certbot to renew a certificate.
To put it blunt: your site is down! You'll need to fix your site so it is UP and so it can serve files in the first place before you continue to get a renewed certificate. Site is currently back up again.