Forward all company calls, FACC feature

there is a trick to doing this.
you need to create a free user(aka a user without a license). Create a custom rule on that user to forward calls 24/7 to that external number.

Then you can do FACC to ext. and select that free user.

It is just the design of the system, that you can forward to an external number only from a user ext. or from a call queue.