Your account will be charged for each request.
The cost can be calculated on the Pricing page.
App Store App Competitors Live
This endpoint will provide you with a list of mobile applications that intersect with the target app for its ranking keywords on App Store. You will obtain the IDs of competitor apps along with search volume and ranking data on competitor ranking keywords.
The returned results are specific to the app_id specified in a POST request. 
The app_id parameter can be found on the App Store website as a part of a URL pointing to a specific mobile application. It consists of numbers indicated after id in the URL string. For example, here is the URL of the TikTok app on App Store:
https://apps.apple.com/us/app/id835599320
The app_id of this app is 835599320