Using the Letsencrypt addon for subdomains

I’m using the official Letsencrypt addon to generate a certificate for my HA installation that is on
I tried adding a subdomain to the config for (so 2 domains in the addon’s config), but this renders an invalid cert and a ERR_CERT_COMMON_NAME_INVALID on the browser’s side.
Can we use/config the addon for this purpose?

I don’t know can you use letsencrypt addon for subdoamains certs. I’m using nginx for a domain and subdomain certs.