Use the contact address of the call to be transfered instead of the
To-header as detailed in the example of section 7.3 of RFC5589: https://www.rfc-editor.org/rfc/rfc5589#page-24
To-header as detailed in the example of section 7.3 of RFC5589: https://www.rfc-editor.org/rfc/rfc5589#page-24