business method patents for fintech startups

Business methods can be patented so long as the "invention" involves more than some abstract idea thinly veiled as being accomplished on a computer. Whether your particular technology is patentable is a question whether it is (i) patentable subject matter, in light of statutory requirements and recent case law (e.g., Alice Corp) and (ii) sufficiently novel and non-obvious over the prior art.

Source code can be (thinly) protected under copyright, but generally your ability to stop someone from "doing" what you are attempting to do is to have patent rights to just that. A reasonable first step would be to speak in private with a patent attorney who can render an opinion on the patentability of your technology prior to pursuing what could be a costly, even if unsuccessful, patent prosecution.

In addition hiring an attorney, I would also strongly recommend that you get a subject matter expert involved to help you identify the best aspects of your invention to patent and help steer you around the prior art. They can also review your claim language through a technical lens. All of this would be extremely important if the patent is ever litigated, as many highly successful patents often are.