I tested it with some Meizu smartphone with QQ Music, using simple USB-C to USB-A adapter and stock USB cable, worked fine without any special needs.
When you connect UP4 to your Xperia, does the LED at least light up red?
Neither the Xperia nor UP4 has any change when I connected them together. Only when I put an USB hub in-between, then they responded. This is the same for UP2. This doesn't happened to any other BT adapter that supports USB DAC function, including BTR5, BTR3, ES100, etc.