Problems with Rekordbox and Iphone. The app can't find any song in my device

Hello, I'm Nacho from Argentina. First of all, sorry for my bad English. I am having problems with the latest mobile version of rekordbox on my iPhone. I recently acquired a DDJ-FLX4, and the software on my phone doesn't seem to allow me to bring the songs stored on my phone. Has anyone had the same problem? Is this specifically an iPhone issue? My iOS version is 16.1.1. The upload button is light grey and doesn't work either. Please help...