We operate a voice application that accepts incoming calls and forwards them later. When forwarding, several values are to be transferred via custom headers of the SIP REFER messages (we use BLind Transfer here). We have already configured the SIP line headers in CIC, once as transferred headers and also as call attributes. However, the headers are not filled after forwarding in CIC. It seems as if the values are not transferred.

We use an external SIP library for call processing in our application. Currently we don't use the IceLib for Blind Transfer, because we can't map the incoming SIP call via the SIP library with the interactions we see with the IceLib.
In an incoming INVITE I see a custom header from the CIC "x-inin-crn" with an InteractionId that is higher than the actual InteractionId that is visible in the InteractionQueue.

My questions are:
1. is it even possible to transfer custom headers to the CIC server via the SIP REFER message? If so, what do you have to consider that we may have overlooked?

2. if the first point does not work, how can we map a mapping between SIP INVITE message and incoming interactions that we see with IceLib? Is it possible to pass custom headers to an INVITE message via CIC? Or is there any way to get the SIP Call-Id via IceLib?