Scenario

Assume the API returns JSON like this:

{
  "accessToken": " 1 1 s+Z"
}

Goal

Save the accessToken to a Postman environment variable.

Implementation

Add the following code to Postman’s Tests tab:

var jsonData = JSON.parse(responseBody);
environment.set('access_token', jsonData.accessToken);

Result

Switch to the target environment to verify that access_token is now saved.