I struggled for a while on this and found various hints across the Internet but nothing complete - hope this helps.
Modify the Influx configuration file to use the letsencrypt certificates
https-enabled = true
https-certificate = "/etc/letsencrypt/archive/domain.com/fullchain2.pem"
https-private-key = "/etc/letsencrypt/archive/domain.com/privkey2.pem"
Permissions need updating to allow influx user to access certs
usermod -G certusers influxdb
chown root:certusers /etc/letsencrypt/archive/
chmod 750 /etc/letsencrypt/archive/
chown root:certusers /etc/letsencrypt/archive/domain.com/privkey2.pem
chmod 640 /etc/letsencrypt/archive/domain.com/privkey2.pem
ESP sketch can be found here → Tobias Schürg ESP8266 sketch
Thank you for this example!