CXone Personal Connection API returning 400 on outbound call POST

We’re hitting a 400 on POST /api/v2/interactions/outbound/calls when trying to trigger an outbound call through the CXone Personal Connection API. The Rust service builds the request fine but the response comes back blank with just the status code.

{
 "to": "+12125551234",
 "personalConnectionId": "pc-8923",
 "from": "direct-dial"
}

Seems like the personalConnectionId mapping is broken or we’re missing a hidden param.