It depends a bit on what equipment is used, controller, Instant AP, AOS10, switch (and type/brand).
But if the question is about an automatic redirect from the receipt page to the login page, then there are examples with javascript to do such an automatic redirect.
If it is about redirecting to your own website, regardless of what triggered the initial redirect, then some access methods allow override of the URL, or you can do it in the NAS Vendor Settings in your Self Registration Workflow:

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Herman Robers
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If you have urgent issues, always contact your Aruba partner, distributor, or Aruba TAC Support. Check
https://www.arubanetworks.com/support-services/contact-support/ for how to contact Aruba TAC. Any opinions expressed here are solely my own and not necessarily that of Hewlett Packard Enterprise or Aruba Networks.
In case your problem is solved, please invest the time to post a follow-up with the information on how you solved it. Others can benefit from that.
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Original Message:
Sent: Nov 09, 2023 04:51 AM
From: Bob Magic
Subject: SMS Authentication Clearpass Guest
Thank you, it works now. But I have a question. In the video, at the end the user is not redirected to the portal. Do you know how can I change the redirection of the receipt page ?

Original Message:
Sent: Nov 08, 2023 11:31 AM
From: Herman Robers
Subject: SMS Authentication Clearpass Guest
Yes. Video.
Just note that some (IOS) devices suffer the issue that when you open your SMS application, you can't get back to the captive portal.
------------------------------
Herman Robers
------------------------
If you have urgent issues, always contact your Aruba partner, distributor, or Aruba TAC Support. Check https://www.arubanetworks.com/support-services/contact-support/ for how to contact Aruba TAC. Any opinions expressed here are solely my own and not necessarily that of Hewlett Packard Enterprise or Aruba Networks.
In case your problem is solved, please invest the time to post a follow-up with the information on how you solved it. Others can benefit from that.
Original Message:
Sent: Nov 08, 2023 10:29 AM
From: Bob Magic
Subject: SMS Authentication Clearpass Guest
Hello,
I would like to know if it was possible to authenticate with SMS on Clearpass.
For example :
1. A user arrive on a web page when connecting to the open wifi.
2. A form ask the user his phone number.
3. When he submit his phone number, a code is sent on his phone.
4. A new form ask him the code.
5. And then he is authenticated and has internet access.
Have you ideas about this method ?