Web GUI request rejected

I have a fresh install in a TrueNAS core jail. Plenty of storage capacity in the pool that has a correct mount point. Have looked at the jail log, nothing. I have tried both plugin install, and manual install in a jail with the same result–A rejected request for the web GUI. I can ping the jail, so that indicates network success. All other jails, with the exact network configs except IP, of course, are available, indicating not a firewall problem in the router.

Any suggestions appreciated.