Domaing Mapping NOT redirecting subdomains to custom domains

Subdomains: subdomainname.mywebsite.com is not redirecting to custom domain: subdomainname.com..... Please check:
<p>Mywebsitelink </p>
<p>A subdomain example</p>
<p>A domain for the subsite</p>
Please advice, this is CRITICAL!

thank you.