Open Messaging API: Quick replies returning 400 Bad Request

Trying to send a structured card with quick replies via POST /api/v2/conversations/messages/{conversationId}/communications/{communicationId}/messages. The text payload works fine, but adding actions fails with a 400.

Payload looks like this:
{
“text”: “Choose an option”,
“actions”: [
{
“type”: “quick_reply”,
“label”: “Option 1”,
“value”: “opt1”
}
]
}

The docs say actions is valid for webmessaging. Error body just says Invalid request. Missing something obvious in the schema?

The actions array needs to be wrapped in an elements object. Try this:

{
 "text": "Choose an option",
 "elements": [
 {
 "type": "card",
 "elements": [
 {
 "type": "quick_reply",
 "label": "Option 1",
 "value": "opt1"
 }
 ]
 }
 ]
}