Services
Payments
You'll need cloud functions to work with their APIs, but these services are perfectly well suited for that.

Braintree
Chargebee
Think of Chargebee as your off-the-shelf, plug-and-play billing solution delivered on the cloud.
With Chargebee, you can set recurring billing frequencies and get paid automatically by your customers. You can easily combine recurring, one-time, and usage-based pricing models.
Chargify
A “Revenue Management Framework” to help with payments and be flexible, like run pricing experiments, handle discounts, personalize offers, and provide insight along the way.

MoonClerk
A no-code-required solution for accepting recurring payments for stuff like digital products, gym memberships, dog walkers, etc.

PayPal
Something like PayPals very simple Buy Now buttons where you send users to PayPal’s websites to buy things, and they are redirected back, are a good match for a static website.
Recurly
Recurly is a SaaS-based company providing recurring billing management. Choose from multiple billing models, payment gateways, and payment options.
Square
Probably the second most beloved payment service out there, with good clean APIs for dealing with payments, customers, and subscriptions.

Stripe
Probably the most beloved payment service out there, with good clean APIs for dealing with payments, customers, and subscriptions.
They even have nice checkout forms you can use, but you’ll still need cloud functions to do all the secure API work.