And one more thing -- by default, vSZ uses encryption for information in this POST, it is also described in manual. So in the beginning turn MAC address encryption off (cli command on vSZ node console, look in the manual) and get things work without encryption. You can deal with encryption later.
There are 2 possible problems:
1. Certificate. If your WISPR server doesn't have public SSL certificate (or SZ doesn't have full chain to trust it), this will fail. To check this, switch to http (port 9997), if it will work than, it is defenitly certificate issue. To make self-signed certificate work, you probably need to import it's CA into vSZ.
2. Check that "NAS IP" is set properly in WLAN configuration to "controller IP" (Radius options, visible only when Radius accounting is set on, but work even if accounting later is disabled). It is possible that POST is sent to other node, which doesn't know about that client.
Hope it helps.