Hi @Chilli-Paul23,
In addition to the links provided by @Inderdeep, I recommend searching for ready-to-use captive portal solutions on the Cisco Networking App Marketplace.
Once you have the External Captive Portal (EXCAP) solution selected, I would recommend to go through this documentation to set this up in the dashboard.
If you're facing any issues while deploying the EXCAP, I would recommend this article. It describes traffic flow in detail and may help you understand where exactly the flow breaks.
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