GDbus.Error:org.openobex.Error.Failed: Unable to request session problem

If you run "bluez-simple-agent" (terminal or Alt + F2) you can send files.

It's a bug

There is a open bug report about this.

Apparently you can work around the problem installing and using blueman.

I received this error message too when trying to send files between laptop and phone, but it wasn't solved by using a different method of sending/receiving.

I could connect and 'pair' my device, however I couldn't send any files. The problem was solved by finding and killing some other interfering processes. I can't explain why is worked, only present my solution.

I used "airmon-ng check" to find the processes, which I then killed:

:/#   airmon-ng check
Found 3 processes that could cause trouble.
If airodump-ng, aireplay-ng or airtun-ng stops working after
a short period of time, you may want to kill (some of) them!

PID Name
17689 NetworkManager
17694 wpa_supplicant
17696 dhclient

I then used the "kill" command for each of these in turn:

:/#  kill 17689
:/#  kill 17694
:/#  kill 17696

I did try to do it more methodically at first, only killing one at a time to check if I could then send a file, then two of them (working through all combinations) - however it only worked after all three were "killed".

I hope this helps somebody!!