[asterisk-users] Billing number vs. CallerID number | Asterisk 11.5.1

[Positively Optimistic]

In a multi-tenant environment, we are sending various CallerIDs outbound
from asterisk based on who the user is.  We have an insurance agency who
would like to present a toll free callerid.  This works..  unless they're
calling a toll free number.  In that case, occasionally, the call fails.
 However, should we send a correctly formatted npanxx of a local number,
the call completes.

We have been advised that we can send the billing telephone number as a
separate header and the call will complete, all-the-while, presenting the
toll free number as the caller id.

Does anyone know of the correct header required to provide this
functionality?
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