If you don't choose to write your own software using your own data, that's cool; you can buy that software from us, for two cents a transaction (or less).
We're a software company selling to software developers. We're cool with you writing your own software with your own data if you think your engineers are sufficiently efficient at this to make that the best possible use of their time. (The businessman in me suggests that it is extremely unlikely you can profitably employ engineers to write this software at most likely scales of your business and, contingent on being able to do that, it is quite likely there are a hundred better projects not upper bounded at 2 cents a transaction, but you are a project away from constructively disproving this if you strongly disagree.)