Hi @robinmonjo
that's not a Letsencrypt error, that's a check of cert-manager.
Cert-manager expects http status 200, but sees a 503.
But curious: There are checks of your domain, ~~20 minutes old - https://check-your-website.server-daten.de/?q=nantes.apecconnect.apec.fr
There is no http status 503 visible.
-->> check, if there is an update, perhaps an internal bug.