I had one of the dongles go missing, and I tried another nano dongle and it worked good, so they aren't propitiatory,
so possibly try a different one to test if it's the dongle or something else. The brand I used is a TpLink TL-WN725N.
Even if it's just borrowing a larger wireless adapter for the test. To see if it's tablet or dongle compatibility, does the mixer connect to the internet for firmware updates ?
Assuming it's the correct settings on the app you installed and the mixer, I'm assuming the unit is a Touchmix, but the heading doesn't specify.
I'm using Android, but the dongle part of it shouldn't care if Android or Apple.