sudo certbot certonly --standalone --rsa-key-size 4096 --agree-tos --preferred-challenges http -d your_domain
try to disble nginx for a while and then start it again
service nginx stop
service nginx start
sudo certbot certonly --standalone --rsa-key-size 4096 --agree-tos --preferred-challenges http -d your_domain
try to disble nginx for a while and then start it again
service nginx stop
service nginx start