Postman is an API client tool which helps to test the API's. It enables us to test the same request against different environments with environment specific variables.
Get the postman client - https://www.getpostman.com/
Have a look in ONAP documentation here : https://docs.onap.org/en/dublin/submodules/integration.git/docs/docs_postman.html
Step 1: Add the APPC collections to the postman
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Select any API and click Send.
Hoorayyy !!!!. Now its easy to test the same api against different environments just by selecting in the environments drop down.