How to get pn-prid with PJSIP_HEADER in Asterisk dialplan

Question

In extensions.conf i have a context

[from-internal-custom]
exten => _X.,1,NoOp(Exec script)
exten => _.,n,System(go run /callkeep/tools/main.go -i ${CALLERID(num)} -p fcm -d PJSIP_HEADER(read,contact)}) 
same => n,Goto(from-internal,${EXTEN},1)

I can get the contact with this script, but i want to get pn-prid in a header like this

Contact:<sip:[email protected]; pn-provider=acme; pn-param=acme-param; pn-prid=ZTY4ZDJlMzODE1NmUgKi0K>;

PJSIP_HEADER(read,contact) returns just sip:[email protected]

i try PJSIP_HEADER_PARAM(Contact,header,pn-prid) this return null