Try something simpler:
nslookup acme-v01.api.letsencrypt.org
If that fails, there is the reason this fails.
If that is successful, try:
curl https://ipv4.address
curl -6 https://ipv6.address
For IPv4 I get:
curl https://23.219.99.47
curl: (51) SSL: certificate subject name (*.api.letsencrypt.org) does not match target host name ‘23.219.99.47’