A filtered header of a call in a Gateway-Gateway (GW-GW) scenario is not passed to the egress gateway if that header is known to the egress gateway, even if the "unknown" header transparency is enabled.
For example, the P-Asserted-Identity (PAI) header is not passed transparently if the following events occur simultaneously:
the PAI is filtered on the ingress
the "unknown" header transparency is enabled on the egress gateway
the PAI header is known to the egress gateway.
To pass the PAI header transparently on the egress gateway, enable transparency for the PAI header through a SIP Filter Profile.