The Spreedly iOS SDK by Spreedly supports ApplePay to integrate payment features by working with the API. Installation via CocoaPods. Running tests available.
Follow this tutorial and in around five minutes you could have a simple Java command-line application that is able to make requests to the Google Apps Script Execution API.
Switch announced the CardSavr API which allows credit card details to flow directly from the card issuer to thousands of ecommerce sites. Once integrated, updated card information can be sent to the selected sites without users needing to reload the information, or card issuers to reissue cards.