Open Messaging API: Quick Reply cards rendering as plain text in Custom Agent Desktop

We’re pushing structured messages via the Open Messaging API for a new webchat flow. The payload includes quick_replies and cards, but our Custom Agent Desktop just renders them as raw JSON text blocks. The HTTP 200 confirms the message was sent, but the client_app_sdk isn’t parsing the contentType.

Here’s the payload snippet:

{ "contentType": "application/vnd.genesys.messaging.quickreply+json", "content": { "items": [...] } }

Tried changing the encoding headers, no luck. Is there a specific client-side config needed to handle this?