I use to run this command for get new certificate : ./certbot-auto certonly --rsa-key-size 4096 --non-interactive --standalone --email admin@$(hostname --fqdn) -d $(hostname --fqdn) --agree-tos
I always use the FQDN name of my VPS or server but in this case with the domaine *ovh.net i got an erreur :
Too many certificates already issued for: ovh.net
Let's Encrypt limits the number of certificates that can be issued to the same registered domain (a registered domain is basically a TLD + the next DNS label, so for example.ovh.net that would be ovh.net). More details here:
Unless you can talk OVH into adding their domain on the public suffix list, you'll need your own domain name. A free option would be .tk with CloudFlare as a DNS provider.