Incomming call transfer to external number

On my SipX 3.4 using my polycom 601 I can transfer an internal call to an external extension but trying to transfer an external call to an external number isn't working.

Does anyone know how to resolve this or what I might be doing wrong?

Is it even possible?

RESOLUTION:

1) Create new users in the configserver for specific use with your AudioCodes Gateway.

2) Then in your AudioCodes webUI (Protocol Management>Endpoint Settings>Authentication) inpute the user name and password you just created in your SipX configserver.

After that everything worked just fine.