I tried to use the Postman collection of WSO2 API Manager to work with APIs, but it didn't work fine and it return for all API 404 Not Found ,when i try to click on the red button it shows the error "Unable to verify the first certificate" .
Go to Postman settings and try disabling SSL Certificate Verification.
Update
It seems you are using the wrong version of the API. The publisher Rest API version for API Manager 4.1 is v3. Can you try downloading the collection from here.