Perhaps it will be useful for someone, I couldn’t find the solution for this.

So with fresh Unifi Flex switch, I’ve tried to adopt it with ssh “set-inform http://ip-of-host:8080/inform”. I’ve put IP address of my Unifi Controller in place of “ip-of-host” of course.

The switch shown as ready for adoption in Network Controller, but when adopted it became offline. It was steady blue light on it, so switch reported “adopted”. It was pingable from controller, I could ssh to it, ports where open and so on. Other AP’s on the same network vlan where also fine and previously configured without an issue.

I’ve tried to factory reset it and adopt again – same result.

But when I’ve looked in to the logs on flex I saw this:

Thu Aug 7 07:47:10 2025 daemon.err mcad: mcad[1204]: ace_reporter.reporter_fail(): Unable to resolve (http://unifi:8080/inform)
Thu Aug 7 07:47:10 2025 daemon.err mcad: mcad[1204]: ace_reporter.reporter_fail(): initial contact failed #2940, url=http://unifi:8080/inform, rc=1
Thu Aug 7 07:47:10 2025 daemon.info mcad: mcad[1204]: ace_reporter.reporter_next_inform_method(): next inform family: 10

So despite informing flex it should use IP to connect to the controller – and it used this information since it reported to it – after adoption process start it again wanted to use DNS name for connection. And it failed – since it was not defined this way on my domain/search domain.

So as a quick fix, I’ve added to the flex /etc/hosts line pointing unifi to the right IP and adoption finished. What’s surprising – later on, after adoption was finished correctly – the flex was using again the IP for connection, not the name… strange :/