Or if you don't know what a response is, you can always write a webmention comment (you don't need to know what that is).

Webmention Rocks! said: This test verifies that you accept a Webmention request that contains a valid source and target URL. To pass this test, your Webmention endpoint must return either HTTP 200, 201 or 202 along with the appropriate headers. If your endpoint returns HTTP 201, then it MUST also return a Location … β€” 30 Dec 2019 21:38