Once your account is created, download the Loadmill Test Composer Chrome Extension. This extension allows you to compose your test scenario by registering your API requests while you navigate the site. It will register any type of API requests being sent and received from the server.
You can also apply specific filters if you want to register requests relevant to your test case flow. As well as adding domains in case you want to register our-of-domain APIs such as third-party APIs that is necessary for completing your flow. See the Test Composer Setup for more info on the composer features.