I ran into an issue where nginx was misconfigured and didn’t want to start (kept failing the same nginx.conf test looking for missing files in my /etc/letsencrypt) because I only copied what this thread suggested : archive, live and renewal folders (namely by @bmw).
Initially I thought this would work but I was wrong.
Certbot kept complaining there are two other files missing: ssl-dhlparams.pem and options-ssl-nginx.conf which were utterly missing from a new certbot install via apt certbot ppa
Just wanted to let other people know they have to copy these two extra files in order to migrate with no hassle.
After that, running certbot --nginx asked if I wanted to install existing certs and from there the wizard took care of everything.
Bonne chance