Point subdomain to firebase hosting

I have Godaddy hosting. My requirement is simple, I need to point app.example.com to example.web.app For that I have done these steps I verified the main domain with the txt entry. I also did a txt entry for that sub domain I created A records with the IP's provided by firebase where host is app.example.com Godaddy team said we need to create a CNAME, so we also created a CNAME entry where Name is app and value is example.web.app Do i need to do anything else ? Shall I keep this CNAME entry or delete it ? Its opening my link now but saying **This page is not secure (broken HTTPS).**, cretificate missing, issued to firebaseapp.com What else do I need to do to make it work with https?