I can't delete my domain because of an associated Let's Encrypt certificate

DNS domain is currently in use by a Let's Encrypt certificate

You cannot delete a domain if a Let’s Encrypt SSL certificate is still associated with that domain.

To resolve this error, delete the SSL certificate associated with the domain you want to delete and then retry deleting the domain.

You can renew your certificate manually using Certbot.
You can typically install an SSL certificate by adding a few lines of configuration to the Droplet’s web server, or by using tools that automatically add the configuration for you.