create accounts

I'm trying to create new accounts programmatically using the Adwords API on our app. We're planning on using ManagedCustomerService to do so. From my research it seems like we only need 3 inputs fro

AuthorizationError.NO_CUSTOMER_FOUND

We are getting this NO_CUSTOMER_FOUND when trying to get all Google Ads accounts of a user. The user grants permissions to our app and then we have to display a select box where they can chose which Google Ads account they want to use with our app. We are using the Python Library of the Adwords