Open Messaging API: Quick replies not rendering in guest widget despite valid payload

I’m building a custom agent desktop extension that needs to push structured content back to the guest during a Web Messaging session. The goal is to send a card with quick reply options using the Open Messaging API. I’ve been constructing the payload manually because the SDK helpers seem a bit limited for complex card structures.

Here is the JSON payload I’m posting to https://api-eu-west-1.genesyscloud.com/api/v2/conversations/messaging/conversations/{conversationId}/messages:

{
 "content": {
 "type": "application/vnd.genesys.messages.card",
 "elements": [
 {
 "title": "Select an option",
 "description": "Please choose one",
 "actions": [
 {
 "type": "quick-reply",
 "label": "Yes",
 "value": "true"
 },
 {
 "type": "quick-reply",
 "label": "No",
 "value": "false"
 }
 ]
 }
 ]
 },
 "from": {
 "id": "{agent_user_id}",
 "name": "Support Agent"
 }
}

The API call returns a 201 Created, and the message ID is returned successfully. However, when the guest views the message in the widget, they just see a blank space or a generic text bubble with no interactive elements. The quick replies don’t render at all. I’ve checked the network tab, and the response from the server matches what I sent.

I suspect the type field in the content object might be wrong. The docs mention application/vnd.genesys.messages.card but I’ve also seen references to application/vnd.genesys.messages.quick-reply directly. Is there a specific schema version I need to specify? Or am I missing a required field in the elements array? The widget version is 5.2.1. Any ideas on what’s breaking the rendering?