Creating Mobile Messages
Messages give you a way to organize creatives by grouping them together, regardless of the channel or device for which the creatives are designed. Messages typically contain more than one creative. Creatives of different types can be in the same message. For example, a message can include an HTML creative and a mobile in-app creative.
Only HTML assets can be the source of a creative. Mobile in-app messages and push notification messages use images, not HTML. Therefore, the option to import an asset as a creative is not applicable to mobile in-app or push notification message creatives. The option is applicable to HTML creatives that deliver content to mobile spots.
A message and its creatives can be added to a task only once the message is marked ready or is published. For more information, see the following documentation: