"Socket type not supported" with OTP

[BuzzSaw Code]

I've setup some new RHEL8 KDCs that will use the otp feature - I have
this working on RHEL7 without issues.

But on the RHEL8 hosts I'm getting "preauth (otp) verify failure:
Socket type not supported" errors.

Each KDC has a local radius server listening on the IPv6 loopback, so
the kdc.conf has this for the otp config:

[otp]
   DEFAULT = {
        server = localhost6:1812
        secret = mysecret
        strip_realm = true
   }

Is there a way to debug the KDC process further to see why it doesn't
like that loopback without building a custom debug kdc ?