That may depend on the type of WPA3, if it's personal (SAE) or Enterprise. iPhone 5C seems unsupported/unmaintained since 2017, which is well before WPA3 and also before some modern encryption algorithms used today in WPA2/3 Enterprise.
Some devices are incompatible with transition mode, this may be one.
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Herman Robers
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If you have urgent issues, always contact your HPE Aruba Networking partner, distributor, or Aruba TAC Support. Check
https://www.arubanetworks.com/support-services/contact-support/ for how to contact HPE Aruba Networking TAC. Any opinions expressed here are solely my own and not necessarily that of Hewlett Packard Enterprise or HPE Aruba Networking.
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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