[Freeswitch-users] User-to-User RFC 7433

Hello, I need to add the User-to-User field to the SIP header - for incoming calls. I have not managed to do it (neither for incoming nor for outgoing calls). In ./conf/dialplan/default.xml, <extension> section, I added : <action application="set" data="sip_h_User-to-User=123"/> or <action application="set"><![CDATA[sip_h_User-to-User=${sip_Call_ID};tenant=1101;DID=${sip_to_user}]]></action> No result. In sofia_presence.c, I've seen some code for "User-to-User", so it should be possible. But how to do it ? Best regards, Adrian.