If not done already, install Spotipo on your sever by following tutorial available here.
Make sure you have enabled ports 1812 and 1813 in your firewall for UDP traffic.
Add an Aruba Central Site in Spotipo
Each location is represented by a Site. A site can have multiple routers (of the same type)
After adding the client add a new site by clicking on the Add New Site button in the drop down menu on top right.
Select the Site type as Aruba Central and configure the correct timezone and Save
Now proceed with site activation and license subscription.
Add a Network
In the newly created site, navigate to Networks tab and create a New Network.
Provide a name to identify your network
After adding the network, take a note on the URL, NAS ID and Radius Secret
Configure Aruba Central Network
Log into Aruba Central and navigate ti Networks Tab. Press add new Network
Configure the SSID you would like to have and select the type as Guest
In the security tab select the Splash Page Type as External and press the + button to add new captive portal profile
Provide a name to identify the captive portal profile. Also configure the hostname of your spotipo server and the URL generated in previous step.
Also check the box to include VC IP in redirect URL.
Configure Radius Server
Add a new Authentication server as Primary Server
Provide the details of your spotipo server. Also fill in the NAS ID and Radius Secret generated in last step.
Enable accounting and authentication and save the profile
Enable accounting to same servers with accounting interval as 1 min.
Enable Walled Garden
Add hostname of your Spotipo server into walled garden.
Save And Test
Click Next and Save the configuration. Wait for a few minutes and then connect to the SSID you have just created to test it out.