We've built it using the Strike API. The main challenge here was upgrading the protocol to be usable with multiple denominations and payment methods. As of now, you can use "USD" ecash to pay and receive on Lightning as long as the backend can convert it (which is what Strike does).

I'm going to build an alternative to the Strike backend using stable lightning channels though (using 10101 or StableChannels on CLN) - that means no third party needed anymore!