Migration Assistant Not Working

Have just a new macbook air and trying to use the migration assistant to transfer wirelessly over from my 4 year old imac.

Both macbook and the imac have their firewalls turned off but they seem to can't find each other on the same wifi network. The imac briefly appeared once on the macbook however once I clicked continue there were errors.

Macbook is running the latest OS while Imac is on an older version (3-4 versions old) thought security updates are the latest.

Any suggestions on how to fix this?