That's a great question. Here are some things to consider:
Research the integration methods of the software. They don't all work the same.
2. Processing Fees
This is a very unregulated market. The fees fluctuate greatly. Know the differences between the major card processors.
How much money do you have to send on this? There are free versions that take money on the back end (usually higher) and paid versions that take less on the back end).
Does that help answer your question?
-Mario Ashley, MBA
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My consulting company, while building software for all types of industries, we 100% use Stripe at first. It's part of our process, so we know why and how to integrate it well.
It sounds like you are building your platform, which means you don't have any customers currently, which also means you don't have to worry about processing fees. The main thing you want to do, is make sure you use a Service Object to wrap Stripe code with, so you can change this down the road (much much farther down the road when you're doing 100's of 1000's in transactions per month) so you can move to a different provider for a cheaper transaction rate. Like I said, thats overkill to even worry about right now. Just use Stripe.