Comment 69 for bug 1748565

$ tail -f /var/log/syslog
Dec 1 21:28:26 localhost kernel: [ 683.235091] Bluetooth: hci0: last event is not cmd complete (0x0f)

$ dmesg | grep -i bluetooth
[ 3.368473] bluetooth hci0: Direct firmware load for brcm/BCM20702A1-13d3-3404.hcd failed with error -2
[ 3.368475] Bluetooth: hci0: BCM: Patch brcm/BCM20702A1-13d3-3404.hcd not found

I use the step to fix, now I can send file to my phone with bluetooth, and use AirPods :)

https://unix.stackexchange.com/questions/359979/broadcom-bcm4352-bluetooth-does-not-connect?answertab=votes#tab-top

my step:
$ cd /lib/firmware/brcm
$ sudo wget https://github.com/winterheart/broadcom-bt-firmware/raw/master/brcm/BCM20702A1-13d3-3404.hcd
$ sudo modprobe -r btusb
$ sudo modprobe btusb