SIP TO: is needed to change a user domain name

Hi Gurus.

I faced configuration issue.
Please, let me direction which I can digg to.

My asterisk gets incomming SIP call from soft phone.
Asterisk knows a calls of this subscriber have to be forvarded to soft switch accorging with configuration:

exten => t213,1,Dial(SIP/${EXTEN}@soft-switch-out,60,rt)

defaultuser=t138 ; Authentication user for outbound proxies

Asterisk does it.
But on soft switch side I collect traces and see
TO: blah blah blah

The soft switch rejects such INVITE just because it understands domain ‘’ in TO field only.

So … I need to change SIP address in the TO: field somehow.

Is it possible or not?
If yes, how? Do I need to develop some extention or C-programming is needed … or … I don’t know …

Anyway, Any advices would be very appreciated.

P.S. Field FROM: is correct -