Apply JWT to a single API in my project-- not all exposed APIs in the project

I am trying to use JWT with Spring Security and I only want to use the token to authenticate a single API and have all the other API endpoints in my project not need authentication. Right now my authentication works in Postman but when I try to access my /authenticate API in my web browser I get this error:
“There was an unexpected error (type=Method Not Allowed, status=405).
Request method ‘GET’ not supported”
even though when I request mapping for my /authenticate API I am requesting a POST method not GET. I can’t access any of my other endpoints right now until my JWT is authenticated – how do I authenticate my JWT token when I want to open my application in my web browser and not Postman?