Opnsense - only update IPv6 lan prefix

I currently have an issue where I can’t update my IPv6 prefix with the IPv6 delegated prefix available in opnsense.


This update url updates the IPv6 prefix with the /128 address of the opnsense.

The native implementation of dynv6 in opnsense updates my hostname with the /128 of the opnsense.

This is not wanted since I only need to update the prefix. My aaaa records are all MAC address based.

Is there a different variable other than %IP% available in opnsense ?