Action Details
Requirements and how-to articles for Twitter's action:

paid action
An app card image is used in a promoted tweet to encourage users to install/open your app.

You need this to get it done:

File format: Recommended .jpg/.png (.bmp/.tiff not supported) (if you upload a .gif it will be displayed as a static image with no animations)
Maximum file size: 3MB
Aspect ratio: 1.91:1 or 1:1
Image size: 800 x 418 pixels (for 1.91:1 aspect ratio) 800 x 800 pixels (for 1:1 aspect ratio)
Call to Action
The following call to action options are available for app card promoted tweets:
Install (default if app is not installed)
Open (default if app is installed)
App Store Page
The app store page where your app is available to download, and is also where the app title and price will be pulled from.
Tweet Text
Text to accompany the app card and app store link (maximum of 280 characters.)
Requirements missing or found errors? Report

How-To Articles
A list of useful links for you:

Twitter Business - Advertiser creative specifications
Official information on creative specs for ads.
Link missing here or found errors? Improve How-Tos