The Postman API requires you to authenticate all requests with an API Key. This needs to be added to your request in the form of an
apikey URL parameter, or an
X-API-Key header. The API Reference has more info on authentication.
If you're still getting an error, you could have reached your rate-limit of 60 requests per minute. You can confirm this by checking the X-RateLimit-Limit, X-RateLimit-Remaining, X-RateLimit-Reset headers in the API response. More information on rate-limiting can be found in the API Reference.