hi
@Jonathan Hsieh - (disclaimer - I'm from AWS) lot's of "it depends" to this of course, especially on if it's just recurring. I've had a lot of customers with good experiences with Stripe for billing, their API is strong.. Our team wrote a blog on this a while back
Building a Third-Party SaaS Metering and Billing Integration on AWS. Depending on your customers, you may well end out building on Marketplaces like AWS Marketplace. There are some cool tools like Amberflo that can sit between you and these providers, and help you iterate on your subscription pricing... Would love to hear what some other people are doing 🙂