It can be anything! An apex, subdomain, or even a URL.

Results forwww.e2e-test-server.app.render.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2019-03-16T05:41:42.829	2019-03-16T04:41:40	2019-06-14T04:41:40	e2e-test-server.app.render.com	e2e-test-server.app.render.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-03-16T05:41:40.895	2019-03-16T04:41:40	2019-06-14T04:41:40	e2e-test-server.app.render.com	e2e-test-server.app.render.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-01-15T06:40:52.053	2019-01-15T05:40:50	2019-04-15T05:40:50	e2e-test-server.app.render.com	e2e-test-server.app.render.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-01-15T06:40:50.85	2019-01-15T05:40:50	2019-04-15T05:40:50	e2e-test-server.app.render.com	e2e-test-server.app.render.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-11-16T07:39:58.556	2018-11-16T06:39:57	2019-02-14T06:39:57	e2e-test-server.app.render.com	e2e-test-server.app.render.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-11-16T07:39:57.79	2018-11-16T06:39:57	2019-02-14T06:39:57	e2e-test-server.app.render.com	e2e-test-server.app.render.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3