Genesys Cloud Web Messaging SDK: Quick Reply payload structure in Kotlin

Trying to send a structured quick reply via the Open Messaging API from our Android app. Using the Kotlin SDK, I’m constructing a Message object with contentType set to application/json. The JSON payload looks right, but the client receives it as plain text instead of actionable buttons.

val payload = """{"text":"Options","quick_replies":[{"title":"Yes","payload":"yes_click"}]}"""
val msg = Message(contentType = "application/json", content = payload)

Am I missing a specific header or field in the SDK wrapper?