Juniper Mist does not support RADIUS authentication and accounting. Therefore, some reports in the portal like users online now and network reports will be unavailable. Tiered Bandwidth is also unavailable.
Log in to the Mist Dashboard and on the left click Network > WLANs. Click Add WLAN at the top right and configure as per below:
SSID: Guest WiFi (or whatever you wish)
WLAN Status: Enabled
Security: Open Access
Guest Portal: Forward to an external portal
Portal URL: *insert access_url here*
Allowed Hostnames: Please refer to this list.
Click Save at the top right.
Next, go back in to the WLAN you just created and locate the API Secret key. This needs to be set in your WiFi portal under the Venue settings - "Mist API secret" box.