Our dynDNS update interface currently does not support updating the IP address of a subdomain directly.
UPDATE (February 2021): We now support using the dynDNS update inferface on custom domains and on subdomains out of the box. You can use the full domain name (including subdomain) as the update username, and an API token as the update password. (Please note that if you want multiple subdomains always pointing at the same IP, it will be more efficient to create CNAME records for the subdomains using our web interface.) For details, see the docs. /update
However, if I understood you correctly, you would like the wildcard subdomain *.mysubdomain.dedyn.io to point to the same IP address as your main domain mysubdomain.dedyn.io. In this case, you can achieve the same effect by configuring a DNS redirect from the wildcard subdomain to the main domain. You can do that by creating a record with type CNAME and subdomain *, pointing to the target value mysubdomain.dedyn.io..
To set this up, please use the Passwort Reset functionality to set a login password for your account (if you don’t have one yet), log in, click on your domain, and add the record using the web interface.
Please let me know if you run into any problems in the process. Good luck!
