I’m afraid you’re still not using terms that make it possible to help.
Swagger (now OpenAPI) is a language for describing API requests and responses. It can give you a framework for building valid JSON payloads as expected by a remote service. But Marketo doesn’t consume OpenAPI specifications for webhooks. You can use OpenAPI offline to generate sample payloads but you’d still end up pasting them into Marketo.
I think you need to start at the very beginning by explaining what you’re trying to accomplish in detail at a business level, without using tech terms. Apologies if you have used the technologies in question, but it sounds like you’re working on some pretty advanced stuff that you haven’t done yet in your career, and the questions just don’t make sense.