Users are anonymous until they pay. The only identifying information stored is a user's email address since this is how a user is linked to a license subscription. The user's email address is stored on ExtensionPay's server.
No user information or credit card information is stored on Discogs Enhancer's server. No credit card information is stored on ExtensionPay's server. When a user begins paying for a license subscription, this is done through Stripe, so the user's credit card information is stored on Stripe's servers.
Google Analytics runs on the ExtensionPay site but not in the Discogs Enhancer extension itself. Discogs Enhancer does not sell or otherwise give away any user data.
ExtensionPay's privacy policy can be found at ExtensionPay.com at the bottom of the page. Stripe's privacy policy can be found here: https://stripe.com/privacy