What two types of authorization do RADIUS servers offer to a controller?

An engineer has implemented 802.1x authentication on the wireless network utilizing the internal database of a RADIUS server. Some clients reported that they are unable to connect. After troubleshooting, it is found that PEAP authentication is failing. A debug showed the server is sending an Access-Reject message.
Which action must be taken to resolve authentication?

What services does a controller provide during normal operation of FlexConnect access points (APs) in connected mode.

Which channels does the 802.11 standard define for sending multicast frames so that all associated stations can receive them, regardless of what channel width is in use?

Which one of the following makes a controller failure most disruptive to connected clients?