Must be paid subscription, legacy free edition won’t work.

1. First enable API access from your G Suite Admin Panel.

Security > API Reference > Enable API Access

2. Next, from profile section, select new user features to Rapid Release, and new products to Automatic.

Company Profile > Profile

3. Add secondary domain, and make it primary, then remove the existing domain

4. You can try it by a command, click “Try it now”.

https://developers.google.com/admin-sdk/directory/v1/reference/customers/update#try-it