Jira API Returns 401

I am running a GET request (/rest/agile/1.0/epic/{epicIdOrKey}) to get a Jira epic that returns a 401 in the browser.

I was, however, able to get a 200 response in Postman. Is there a reason why Postman would work but we’re not able to get authenticated through the browser?

I’ve followed the Basic Auth guide and used a token with my email and API key in the header of the request.