Add WWW to my glideapp on a subdomain

Dear Gliders,
I use a custom subdomain to access my Glideapp ( For this I use a TXT and a CNAME entry in my DNS settings of the main domain However, some users enter Then a DNS_PROBE_FINISHED_NXDOMAIN error message appears in the browser. Do you know how I can set up WWW support?

greetings from Germany