External Acess to Meetme

Can anybody please help me how to setup external access to meetme conference extension?
Internall extension is accessable but from out side it is not.
I have a DID available but do not know how to use it to forward call to MeetMe extension.

Here is my configuration:

exten => 4083677968,n(call),Goto(ext-outside-meetme,s,1)

MeetMe Number: 2255
exten => 2255,1,Answer()
exten => 2255,n,Wait(2)
exten => 2255,n,Background(ivr/IVR-2255)
exten => 2255,n(authenticate),Authenticate(200)
exten => 2255,n,MeetMe(,dM)
exten => 2255,n,Background(wm-goodbye)
exten => 2255,n,Hangup()
exten => 2255,authenticate+101,Hangup()

exten => s,1,Answer
exten => s,2,Wait(2)
exten => s,3,Playback(please-wait-while-i-connect)
exten => s,4,MeetMe(2255|sc)
exten => s,5,Macro(hangupcall)

Will appreciate your kind help