I created a virtual extension 900 on FreePBX v 10.13.66-10, assigned it a number and outbound routes.
I then created a follow me list of a cell phone.
Saved, applied and then when we call it, we get a busy signal.
Did this a few times, played around with settings always resulting in the same issue.
I know this works, so I went to another server 6.12.65-32, created the same thing and it worked perfectly.