The PayPal Ruby Sample Code by PayPal demonstrates how to work with the API. Examples include authorization, capture, configuration, credit card, invoice, notifications, payment, payouts, image, sale, and view.
Stronghold has released a set of APIs that developers can use to add to apps a variety of payment instruments including Bitcoin, Ethereum, and Lumens. The APIs also allow apps to leverage Stronghold platform capabilities such as generate quotes, trade cryptocurrencies, and get available venues.
SparrowOne has opened access to its managed payments services through its new Services API. The API allows for simple, HTTP POST access to SparrowOne's payment gateway. The API is expected to greatly reduce the time and effort needed for partner and client integration solutions.