Web Messaging Widget 403 Forbidden when migrating Zendesk Chat tokens

General Discussion
1

Does anyone know how to properly map Zendesk Chat’s legacy session tokens to Genesys Cloud’s Web Messaging authentication flow?

We are in the final stages of migrating our support channel from Zendesk Chat to Genesys Cloud Web Messaging. The goal is to maintain a seamless experience for users who started a session in Zendesk but get routed to a Genesys agent. In Zendesk, we used a simple JWT passed via the zChatToken parameter to identify returning users. I assumed Genesys Cloud would accept a similar custom attribute or token in the widget initialization script (genesys.cloud.com/gc-apis/webmessaging/...).

I have configured the Web Messaging app in the Genesys Cloud Admin console and set up the domain allowlist. However, when I attempt to initialize the widget with a custom userId derived from our legacy Zendesk session, the widget fails to load. The browser console throws a 403 Forbidden error on the WebSocket connection attempt to wss://webmessaging-usw2.platform.genesys.cloud/.... The error payload indicates: {"errorCode": "FORBIDDEN", "message": "Invalid or missing authentication token."}.

I have verified that the OAuth client credentials are correct and that the scope includes webmessaging:all. In Zendesk, the token expiration was handled server-side, but Genesys Cloud seems to require a stricter handshake. I am using the latest version of the Web Messaging SDK (v2.4.1).

Is there a specific API endpoint I need to call first to validate the external user ID before initializing the widget? Or is there a known limitation with passing legacy session identifiers directly into the Genesys Cloud widget configuration? Any migration tips for handling this authentication gap would be greatly appreciated. We are currently stuck because users cannot reconnect to their previous context without a full re-authentication loop, which defeats the purpose of the migration.

2

This is caused by trying to pass legacy Zendesk tokens directly into the Web Messaging widget, which expects Genesys-specific authentication headers.

  • Replace the zChatToken logic with a Genesys Cloud OAuth 2.0 client credentials flow.
  • Use the genesys-cloud-web-messaging SDK to inject the new access token via setAuthentication.
  • Map the original Zendesk user ID to a Genesys person record using a Data Action before initiating the session.
3

Check your OAuth token scope configuration on the Zendesk side. This is a common issue during migrations where the SCIM endpoints ignore standard admin permissions if the specific Web Messaging scopes are not explicitly granted. The 403 error often stems from the legacy JWT structure lacking the required genesys-cloud-web-messaging audience claim, causing the Genesys identity provider to reject the token before it even reaches the widget initialization layer.

Verify that the client credentials flow is correctly exchanging the Zendesk session data for a Genesys access token. You must ensure every payload block includes a unique ID field, as Genesys Cloud schemas mandate this for session persistence. The migration process frequently strips these identifiers, leading to authentication failures. Adjust the token mapping logic to inject the new access token via the SDK’s setAuthentication method, ensuring the carrier-specific quirks of the legacy system do not interfere with the new routing logic.