RATE_SIP_HEADER specifies the header name of rate value, which is sent inside SIP message.
See details here: Display of Remaining Credit Time (Parse SIP headers).
The rate is encoded inside SIP response message to INVITE requests, for example:
SIP/2.0 200 OK
CSeq: 2 INVITE
From: ...
To: ...
Rate: 0.05
In above example, SIP message contains a custom header "Rate", which is added by billing system. It has value 0.05
In above example installer-brand.nsi should contain following value:
!define RATE_SIP_HEADER "Rate"