What error do you see?
Because I cannot connect to your domain at all. Are you sure that is the correct IPv6 address?
curl -6 https://mdmtop.duckdns.org:443
curl: (7) Failed to connect to mdmtop.duckdns.org port 443 after 230 ms:
Network is unreachable
nslookup mdmtop.duckdns.org
Address: 2c0f:f3a0:93:889:a00:27ff:fe71:4f8c
What does this show from the machine that is running Tomcat?
curl -6 https://ifconfig.io
Also, Tomcat supports using the .pem files created by Certbot. You don't need to import them into a keystore for Tomcat. See: Can Let's Encrypt output (.pem) be used to generate a tomcat keystore / certstore? - #3 by mcpherrinm