My question relates to the use case of trying to build a simple payment flow where one user (a donor) can donate directly to another user (a recipient) with Bitcoin. To begin with, I would like to manually load up and input 2 addresses that respond to a Donate button and ideally get processed from test accounts on the Testnet blockchain.

I am new to bitcoin development and want to understand the underlying mechanics rather than immediately implementing a more sophisticated and abstracted plugin (e.g. Stripe). Additionally, my preferred language is Ruby so I have been favouring APIs with Ruby SDKs.

So far I have a shortlist of the following APIs:

• Chain.com (https://chain.com/docs/ruby#bitcoin-transaction-overview)
• Blockcypher (http://dev.blockcypher.com/#payments) >> provide direct access to Testnet, not clear how would implement with others
• Blockchain.info (can't link with current rep points) >> may force you to use their wallets

Has anyone worked with these and can provide guidance on which is best to implement the above use case? Other suggestions welcome. Appreciate this could be interpreted fairly broadly but I can try and specify further if you have questions.