The DirectAdmin panel has its own password, separate from the client area. Protect it just as carefully.

Signing in with Login to Control Panel from the client area still works without a code - so turn on two-factor authentication in the client area too (Account → Security).
Change it in DirectAdmin from the user menu (top right). Do not reuse the password of your mailboxes or WordPress.
Advanced Features → Login Keys creates separate keys, e.g. for a developer or a tool, with limited permissions and an expiry date. Safer than handing over your password.