The projector does not project photos or movies from a mobile device with “Photo cast”, or it cannot use the My slideshow function in [Poster]
When the “network isolation” (also referred to as “wireless isolation” or “AP isolation”) function of the access point (wireless router) is enabled, photos and movies in a mobile device cannot be transferred to LSPX-P1. If it's your case, try disabling the network isolation function of the access point (wireless router).
Alternatively, by enabling [Settings] — [Network] — [Wi-Fi Direct] in the dedicated application for mobile devices, you can transfer photos and movies via Wi-Fi Direct without using an access point (wireless router).
Note that when using an iOS device, if the device’s available storage space is not sufficient, it may not be able to transfer files. Also, when the transferring file size exceeds the iOS device’s memory size, it cannot transfer photos.