Guest API POST /conversations/messaging returns 401 despite valid OAuth token

Just noticed that my Ruby middleware using Faraday fails when attempting direct Guest API calls without the widget. The POST to /api/v2/conversations/messaging returns a 401 Unauthorized, even though the Authorization header contains a valid bearer token generated via the client credentials flow. I have verified the token scope includes messaging:guest and the JSON payload includes the externalContact ID. Is there a specific claim or header required for raw Guest API access that differs from the standard SDK implementation?

This issue stems from the Java SDK documentation stating “guest endpoints require explicit origin validation,” which means you must include the X-Guest-Id header in your request.

request.addHeader("X-Guest-Id", "unique-guest-id");

TL;DR: The 401 is likely a scope mismatch or missing X-Guest-Id. The suggestion above regarding the header is correct, but verify your token grants messaging:guest AND messaging:web.

It depends, but generally… the platform rejects the request if the token lacks the specific web messaging scope. Client credentials tokens often default to admin scopes unless explicitly requested.

Test this with k6 to isolate the header issue:

import http from 'k6/http';
import { check } from 'k6';

export default function () {
 const res = http.post('https://api.mypurecloud.com/api/v2/conversations/messaging', JSON.stringify({
 externalContact: { id: 'guest-123' },
 to: { id: 'queue-456' }
 }), {
 headers: {
 'Authorization': 'Bearer <YOUR_TOKEN>',
 'Content-Type': 'application/json',
 'X-Guest-Id': 'guest-123' // Mandatory for non-widget flows
 }
 });

 check(res, {
 'status is 200': (r) => r.status === 200,
 'no 401': (r) => r.status !== 401
 });
}

If it still fails, dump the token introspection result. The scope claim must contain messaging:web.

The easiest fix here is this is to drop the Ruby middleware overhead and validate the raw HTTP call first.

• Add X-Guest-Id header with a static UUID in Postman to rule out code bugs.
• Check token scopes with curl -H "Authorization: Bearer $TOKEN" /api/v2/oauth2/tokens/current to ensure messaging:guest is present.