Preserve specific SIP INVITE headers when setting up a call

1. Brekeke Product Name and Version:
Brekeke PBX, Version 3.5.1.6, Pro
2. Java version:

3. OS type and the version:

4. UA (phone), gateway or other hardware/software involved:

5. Your problem:

In my Voice Control System two specific headers are mandatory to be added in SIP INVITE method. But I could see that the PBX removes them. Is there a way the PBX not to do it?

What kind of headers are they?

Are they always fixed values?

The two headers are "Subject" and "Priority". They are mandatory for Voice Control Systems in Air Traffic Control.

Are they always fixed values?

I asked Brekeke Support Team and they answered:
It works fine.

You can create ARS route at [PBX]->[ARS].
Create a new route, and set like below,
- Patterns IN-----
[Matching Patterns]
To: <needs proper pattern>
From: <needs proper pattern>
Plugin 1: sipheader
Param 1: Subject
Return 1: (.+)

Plugin 2: sipheader
Param 2: Priority
Return 2: (.+)

[Deploy Patterns]
Custom: &caller.header.subject=&p1,&caller.header.priority=&q1

-- Patterns OUT-------
[Matching Patterns]
To: <needs proper pattern>
From: <needs proper pattern>

[Deploy Patterns]
Custom: Subject=&caller.header.subject,Priority=&caller.header.priority

wow nice!