Configuring IPv6 Through A Tunnel Broker Service on pfSense

I’m currently working through the Configuring IPv6 Through A Tunnel Broker Service using HE for the broker. All has worked until I reached Setup LAN for IPv6 section. Following directions, I receive the error below when I try to save.

This is the tunnel info from HE:

The config of the GIF interface:

When I look at the interface’s status it has a /128, not sure that is correct.
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If anyone has any thoughts I would greatly apricate them, I’m a total newbie when it comes to IPv6 and was hoping to get a tunnel setup to learn more about it.

Can you make a suggestion on how to subnet it?

This is the example that Netgate gives in their documentation:
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