Can I connect an Arcam rPAC headphone amp to an iPhone / ipad?

I'm looking for a solution to connect my Arcam rpac headphone amplifier to an ipad. There's an old topic saying that the rpac is compatible only with Windows and MacOS, but it works just fine with any android phone / tablet. When I connect it to the ipad, it is powered by the ipad and I have no error message, the music app works just fine but I have no sound on the headphones. I also have the choice to set the rpac on USB 1 or USB 2, apparently neither works. Does anyone have used this device with an iOS product, please?