If you are referring to the from a technical or developer perspective:
: A new AI Assistant is available in the messaging interface to help sellers generate quick, relevant text replies to common buyer questions. Developer & Application Information Ebay Application
: To build an app that interacts with eBay, you must create a developer account to obtain a unique App ID, Dev ID, and Cert ID. If you are referring to the from a
: In the eBay API, message content (via MyMessagesMessageType ) is often restricted to plain text format , even if the user's overall preference is set to HTML. MyMessagesMessageType - API Reference - Trading API Ebay Application