For your European customers you should likely make it more clear what stripe.js does before urging them to install it on every page of their website. Using it as soon as a user has a probable interest to purchase a product (e.g. when he/she clicks on “Register” and chooses a plan) would very likely be acceptable as a legitimate interest under GDPR, tracking all users even if they don’t have a clear intent of purchasing something and e.g. only want to get information about the product will definitely not be acceptable as a legitimate interest and would therefore require clear consent first.

Why not address it here publicly? I don't think you want/expect everyone observing this discussion on HN to reach out to you.

Oh, offer was made in case GP wants to have a deeper discussion/back-and-forth than is readily achievable with an online forum. Timing constraints notwithstanding, we work hard to answer questions on HN too.