Really? I'm using 11.2.5 too and restarted the phone twice, and still not working
I also tried on my iPad and it did not work either
When plugging the lightning end into my iOS devices with the FiiO cable, I see that the SMSL turns blue and than starts flickering red. I can hear an audible pop as well.
I than try the same exercise with my camera kit cable, and no issues working (just a few occasional pops)
I am sharing these videos so you can see what I mean
Sorry for being all over the place with the camera, I was one handing the recording
Not Working (FiiO Cable)
https://streamable.com/vnf1h
Working (Apple Camera Kit Cable)
https://streamable.com/jtq2r