AFAIK, reverse engineering APIs isn’t illegal. [1] There are some (VC backed) start ups that are open about doing it. Teller API is an example. [2] [1] “Reverse engineering generally doesn't violate trade secret law because it is a fair and independent means of learning information, not a misappropriation. Once the information is discovered in a fair and honest way, it also can be reported without violating trade sec…
What in the world is Teller? Are they an actual company with an actual product? The authentication demo on their website is the exact same as Plaid Link, down to the wording. There isn't even a sign up link or pricing page, but they've somehow raised 4 million dollars [1]. https://techcrunch.com/2020/01/27/teller/
Any small change in any of these APIs completely ruins it for all of their clients. Not even sure if they have a product or service either but again, also not sure who would want that.