This depends on your ISP, but typically the delegated prefix is not really static.
In general case, you should configure dynamic prefix forwarding:
Port forwarding to a dynamic IPv6 address - #2 by vgaetera
Also check your IPv6 connectivity from the same host:
ip route get 1::
ping -6 -c 3 example.org
wget -6 -O /dev/null https://example.org/