Help with HMR to add a VSA (accounting) for Contact portion of header

Greetings!  We have a need to report some information from the Contact portion of an invite into the CDR records.  Specifically, we need the imsi value below (due to the caller-id restriction being on) -

 

Contact: <sip:anonymous@172.21.1.50:5060>;imsi=310410303333650

 

I've writtent the following HMR - but it does not appear to be working and I'm afraid I'm a bit lost.  Can someone help me out?  Thanks so much!

 

sip-manipulation
        name                           VSA200
        description                    
        split-headers                  
        join-headers                   
        header-rule
                name                           storeContact
                header-name                    Contact
                action                         store
                comparison-type                pattern-rule
                msg-type                       request
                methods                        INVITE
                match-value                    .*
                new-value                      
        header-rule
                name                           generateVSA200
                header-name                    P-Acme-VSA
                action                         add
                comparison-type                case-sensitive
                msg-type                       any
                methods                        INVITE