With 'an error' it's hard to say something useful on what's going wrong. If you share a screenshot that may help.
I found this link that describes how to setup external captive portal with ClearPass, so while I don't have any experience with Huawei equipment, it seems to be possible. Did you find/follow that instructions?
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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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