Hmm, Thats weird! it should work with the iPhone 14 Plus. Have you tried restarting the device and then try it again? You can also try to reset the network settings and then try again activating the E-Sim through the “Mijn KPN” app. If you tried these options I gave you and it still doesn't work, then I suggest you going to a KPN Store, an employee there can check what is going on with your device and why it is not activating.