1) All the AP's should be configured in same subnet for auto join, if member AP is running on different subnet, manually need to set the current master IP address IP, in member AP using below :
set director ip xxx.xxx.xxx.xxx
Where x.x.x.x is the IP address of the current master AP.
2) Make sure to manage all the AP's in same firmware version (Member AP firmware should be =< Current master AP firmware). "get version"
3) The country code on all the AP's should be same "get country-code"
4)Login to member AP CLI (SSH), execute 'get discovery-agent' to check the status of 'Discovery Agent, to Enable Execute command 'set discovery-agent enable'. The AP should start sending out discovery packets and join the ZD/Master AP.