[seanwilson]

I use https://paddle.com/ for https://www.checkbot.io/ (a Chrome extension for SEO), primarily because they act as a reseller and handle all EU tax obligations for me. Fastspring and Gumroad are other ones to consider if this is appealing.

Let me know if you've got any questions. Generally you need to list all your requirements, narrow down the payment provider that does what you want and follow their integration guides. You generally integrate your SaaS with them using web hooks.