Forward call with original Call number, please Help

Hello, I have a problem with forward call in trunk with original ID.
Example :
A ---- call ----> B ---- forwarded to -----> C

A nad C are in PSTN
B is extension in my freepbx

My operator write me :smile:

Precondition is that from trunk they send me invite, where caller id (From …) will be A and v requwest-uri/To: will be B

If in the same call I forward outgoing INVITE, whre CLI (From) will be not changed, in reqest-uri/To: will be C and I add Header Diversion: sip:[email protected]_site, where B will be number whitch forwarded the call, then we accept the information about the original number and we forward the number.

But I do not know hou to make it in FreePBX. Can somebody help me ?

Thank you.

And they send me some example but I don’t no whitch config to change …

exten => NUMBER_B,1,Set(CALLERID(num)=NUMBER_A)
same => n,SIPAddHeader(Diversion: sip:[email protected])
same => n,Dial(SIP/[email protected])