Because Live2D Cubism Editor requires license activation, an Internet connection is required.
Note: This information is also listed in the system requirements on the Cubism Editor download page.

Be sure that you are connected to the Internet before starting the Editor.

Because license activation is not possible when use of the PRO version was moved offline, use is limited to 7 days after the PRO version was launched. If the version was automatically switched to the FREE version, you can continue to use the PRO version by launching it again when online.