This firebase cloud function is part of a payment flow, that can be used to collect payment for a software product from a user using a stripe payment link and automatically update the user to a premium user and let the user access the premium part of the app, without having to integrate stripe payment gateway.
medium post about the payment flow - https://ganxesh.medium.com/my-simple-template-to-charge-users-of-your-software-product-af6f28f23b10