I'm dealing with the same supply chain issues that we've all been hit by lately. While my new APs are back-ordered for months, I'm scrambling to find a solution for Wi-Fi to open a new school campus in a week.
What I do have are some old R300s I can use as a stop gap until my order comes in. So far, I've been unable to adopt them into my vSZ running version 126.96.36.199.317. I've downgraded my default zone to 188.8.131.52.695, which is the oldest available in my controller. The 3.6 vSZ release notes say that the R300 is supported but they simply don't show up. These APs were previously managed by a ZoneDirector and were on firmware 9.7.x. I've wiped and flashed with firmware 184.108.40.206.1347 but I still can't get my L2 controller to pick them up.
I've tried setting the controller IP via CLI and I've made sure the scg service is enabled but no luck. From the AP cli, I can ping the controller by IP and FQDN. I've looked through the logs but don't know what specifically to look for to resolve the issue. Is there another firmware I should be using? What am I missing? HELP!