Data Action POST to external API returns 500 despite working in Postman

I’m hitting a wall with a Data Action in Architect. The goal is simple: POST some call details to our internal CRM endpoint and map the response ID back to a flow variable. The C# API side is fine, I’ve tested it in Postman and it works perfectly. But inside Genesys, every call fails with a 500 Internal Server Error.

Here is the mapping I’m using in the Data Action JSON:

{
 "method": "POST",
 "url": "https://internal-crm.example.com/api/v1/calls",
 "headers": {
 "Content-Type": "application/json",
 "Authorization": "Bearer {{auth_token}}"
 },
 "body": {
 "phoneNumber": "{{caller_id}}",
 "timestamp": "{{current_date_time}}"
 }
}

The error message in the Architect log is just “HTTP Error 500”. No details. I tried adding a timeout property but that didn’t help. The endpoint accepts standard JSON. Is there a limitation on the payload size or specific characters in the URL that Architect doesn’t like? I’ve checked the firewall logs and the request never even hits our server. It seems to fail before leaving Genesys. What am I missing here?