Building Plugins - Permissions?

Are these companies creating plugins, or are developers creating them, with the company’s permission?

I want to integrate Western Union into my app so that people can pay their international vendors directly through the app. Western Union’s current API assumes I as a company want to use their API to collect payments from customers to my own company, but I want to enable international payments, similarly to how one could do so with PayPal.

I’ve called Western Union, and they suggested I become an agent. I don’t want to. I’ve also emailed them, and no one has called me yet. I just need to figure out how to integrate the same payment portal on, into my app.

Mostly developers are creating plugin and if a api is public then no permission is needed.