Incomming fax doesnt detect "answer" on ivr

Hello! I have trouble with incomming fax and ivr.
When fax dials to my number it waits till operator will pick up phone and only then sends extension num.
My ivr:

;exten => s,1,Background(custom/welcome-msg)
exten => s,1,Answer()
exten => s,n,WaitExten(5)
exten => s,n,Goto(msk-metal,0404,1)

exten => _X,1,Read(NUMBER,4,n,10)
exten => _X,n,Dial(SIP/${NUMBER},20,m)
exten => _X,n,HangUp()
How to generate ‘answer’ signal for fax?