My understanding is that chan_pjsip only supports the standards recommended method of setting To: and the request URI to the same value, when originating a call.
As you can see, from rfc3261 your ITSP is requiring you to violate a SHOULD level requirement of the SIP RFC, so they cannot expect their service to work with an arbitrary SIP client.
Thanks for the quick answer
I will contact our TSP and tell the to provide documentation to where in the RFC that state INVITE and To is allowed to differ
as according to rfc3261 it violate a SHOULD level requirement
#section-8.1.1.1
"The initial Request-URI of the message SHOULD be set to the value of the URI in the To field. "
section-12.2.1.1
“The URI in the To field of the request MUST be set to the remote URI from the dialog state.”