There's plenty of example. Stripity stripe is an example of one of the better integrated examples and even I've been a bit frustrated with it at times. We're currently stuck on a slightly older version and last I checked, it didn't support the latest version of the stripe API. And that's an example of a library thats relatively well maintained. If you want to use authorize.net for instance, you have to roll your own. (there's a hex package but its still very much in beta). If you wanted to do banking and use Synapsefi, be prepared to roll your own.
Now it wouldn't' be any harder to write these libraries in elixir vs ruby or laravel. The difference is there are well polished libraries for both those platforms you can just drop in and use. That makes what could be a week of work in elixir, about half a day in ruby by virtue of the work largely being done for you already.
If the library doesn't exist for either, then I agree, elixir isn't going to be any harder to integrate.
