0.0.0.0 may be problematic.
Can you try
- a proper internal interface IP e.g. 192.168.0.XX:443 or 10.0.0.1:443 (what do you have on your droplet?),
- do not put 443 port in the external url.
With let’s encrypt it should work seamlessly, unless you’ve temporarily blocked your domain on LE by making too many tries,