Your Python installation can’t verify certs. Does your system have an /etc/ssl/cert.pem or know how to verify certs in general?
Edit: Specifically, the Python lib tries to access https://acme-v01.api.letsencrypt.org/ and needs to be able to verify the cert. /etc/ssl/cert.pem is usually a CA bundle - just as browsers have builtin - that provides the global trust anchor.