Asterisk 13 unable to IAX trunk to 1.8

I just downloaded the latest Freepbx ISO district. I chose Asterisk 13, however I am finding that I cannot create an IAX connection between 13 and my other 1.8 server.

If I recall correctly, I believe there was a similar incompatibility between 1.8 trunking back to 1.4 in the past.

I am wondering if perhaps something has changed in asterisk 13 which makes it impossible to trunk back to version 1.8

Anyone have any ideas on what this could be?