Do subdomains work?

I got this error from https://pinheadmz.proofofconcept.

Websites prove their identity via certificates. Firefox does not trust this site because it uses a certificate that is not valid for pinheadmz.proofofconcept.. The certificate is only valid for the following names: proofofconcept, *.proofofconcept, 142.93.115.133

Error code: MOZILLA_PKIX_ERROR_SELF_SIGNED_CERT

... but the TLD-only URL worked fine: https://proofofconcept/

Could be my certificate parameters but I was hoping *.proofofconcept would work.