We are attempting to send a structured card via the Open Messaging API from our Terraform-managed integration layer. The POST to /api/v2/conversations/messaging/messages returns a 400 Bad Request. The payload includes a valid content object with type: card and an array of actions. The error response is generic, stating Invalid message content. We have verified the authentication token is valid. Does the API require a specific version header or is the JSON structure incorrect? Here is the payload we are sending: {“content”: {“type”: “card”, “text”: “Test”, “actions”: [{“type”: “postback”, “label”: “Click”, “payload”: “test_payload”}]}}