Bridging anonymous calls

[Summer]

I currently have a bridge setup to my mobile phone however anonymous calls do not go through..

The gateway is Telnyx and in sngrep it fails with

SIP/2.0 403 Caller Origination Number is Invalid D35
Via: SIP/2.0/UDP 45.63.27.182:5080;received=45.63.27.182;rport=5080;branch=z9hG4bKap9Bg7X034D0F
Max-Forwards: 57
From: "anonymous" <sip:Default324x@sip.telnyx.com>;tag=FgNZrStm5Svye
To: <sip:(snip)@sip.telnyx.com>;tag=e1N1vZN9tSmBr
Call-ID: 1490a0cb-3707-123b-cd99-560003156b52
CSeq: 50441171 INVITE
Accept: application/sdp
Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, INFO, UPDATE, REFER, NOTIFY
Supported: path
Allow-Events: talk, hold, conference, refer
Reason: Q.850;cause=21;text="CALL_REJECTED"
Content-Length: 0

The documentation for Telnyx to handle this correctly is

Caller ID Number Policy | Telnyx Help Center

A comprehensive guide to the Caller ID Number Policy for Outbound Calls.

support.telnyx.com

How would I go about setting the correct SIP headings? Telnyx wants it formatted like

From: "Anonymous" <sip:anonymous@anonymous.invalid>;tag=12345-6789
P-Asserted-Identity: "Anonymous" <sip:anonymous@anonymous.invalid>
P-Preferred-Identity: "Anonymous" <sip:anonymous@anonymous.invalid>

Should I skip the bridge section altogether and write my own dial plan then transfer to that?

This is all within the Call Centre application so it would still need to continue to work with Ring-All situtations.

I'm still new so apologies for any mistakes in writing this post.
Any help would be greatly appreciated