Flex Messages are messages with a customizable layout. You can customize the layout freely based on the specification for CSS Flexible Box (CSS Flexbox) (opens new window). For more information, see Sending Flex Messages in the Messaging API documentation.
type
String Required
flex

altText
String Required
Alternative text
Max character limit: 400
內容可以選擇Bubble、Carousel
contents
Object Required
Flex Message container
由於它涵蓋的範圍太廣因此我就不細講了，以下是此訊息的限制環境
Operating environment
Flex Messages are supported on the following versions of LINE:

LINE for iOS: All versions
LINE for Android: All versions
LINE for macOS: 5.17.0 or later
LINE for Windows: 5.17.0 or later
These properties are only supported on specific versions on both LINE for iOS and LINE for Android.

Property Supported version
adjustMode property of the text and button 10.13.0 or later
maxLines property of the text 8.11.0 or later
action property of the box 8.11.0 or later
我們可以利用line的FLEX MESSAGE SIMULATOR
進行模擬

Flex Message Simulator (line.biz)