If the iOS application is a UE game, then you should be able to use a LiveLinkProvider (see https://dev.epicgames.com/documentation/en\-us/unreal\-engine/live\-link\-plugin\-development\-in\-unreal\-engine) which uses UDP Messaging to transport Live Link data.
But if the iOS application is not a UE game, then you will have to pick and implement the sender of a supported protocol. For example in 5.6, Unreal supports the OpenTrackIO (opentrackio.org) SMPTE-RIS standard for camera tracking, which seems a good fit for sending the device’s pose.
Prior to 5.6, then you’ll have to pick another protocol, for example LiveLinkFreeD (it supports the 0xD1 packet, see https://www.manualsdir.com/manuals/641433/vinten\-radamec\-free\-d.html?page\=30 or https://pro.sony/s3/2020/08/04144807/BRC\-X1000\_X400\_series\_integration\_manual\_CameraTrackingFunction\_v1\.0\.pdf).