Yealink T30P not forwarding calls

[ITSP]

We have set up a Yealink T30P to forward all calls to an exterrnal number (like in this video:

) but it does not work.

We can see the phone has the call forwarding icon displayed but the phone keeps ringing.

 

[TheodorosG_3CX]

Call fowarding can be more easilly be configured with 3CX User Status and Call forwarding
Why not set the user to DND and forward calls accordingly?