To access the Ads API, developers need a Twitter API key with whitelisted permissions. Follow the steps outlined in this document to register a new API key and retrieve the ID required on the Ads API application form.
STEP 1

Log into Twitter with the @username that will own the API key. We prefer that partners use corporate (e.g. @Twitter) instead of personal handles (e.g. @Jack) for security reasons.
STEP 2

Navigate to apps.twitter.com. Click Create New App.
STEP 3

Complete the form and click Create your Twitter application.
STEP 4

If the app is created successfully, you will be taken to the app’s settings page. The App ID is the number at the end of that page’s URL. See the example below.
I already have an API key - do I need to create a new one?
We prefer to grant Ads API access to new apps without previous API activity. If you submit an App ID with too many active user tokens, access will not be granted and you may need to apply again.