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

Results forapi.bubblebump.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2020-02-04T23:05:50.838	2020-02-04T22:05:50	2020-05-04T22:05:50	api.bubblebump.com	api.bubblebump.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-02-04T23:05:50.598	2020-02-04T22:05:50	2020-05-04T22:05:50	api.bubblebump.com	api.bubblebump.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-02-03T22:49:56.339	2020-02-03T21:49:56	2020-05-03T21:49:56	api.bubblebump.com	api.bubblebump.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-02-03T22:49:56.178	2020-02-03T21:49:56	2020-05-03T21:49:56	api.bubblebump.com	api.bubblebump.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-02-03T22:07:41.677	2020-02-03T21:07:41	2020-05-03T21:07:41	api.bubblebump.com	api.bubblebump.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-02-03T22:07:41.475	2020-02-03T21:07:41	2020-05-03T21:07:41	api.bubblebump.com	api.bubblebump.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-01-29T22:05:02.327	2020-01-29T21:05:02	2020-04-28T21:05:02	api.bubblebump.com	api.bubblebump.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-01-29T22:05:02.125	2020-01-29T21:05:02	2020-04-28T21:05:02	api.bubblebump.com	api.bubblebump.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3