When you change your Google Apps domain on G Suite, Google does not transfer connections to external applications like Insightly, and Insightly does not support multiple domains.
This limitation leaves you with two options when changing your domain:
You can add your new domain to G Suite and continue to use your existing Insightly account with the old domain logins and email addresses. Here is a link to Google's documentation.Insightly does not support multiple domains.
You can export your main records from your old Insightly account and import them into a new Insightly account. You can read more about transferring your data in this article.
If you have a paid subscription to Insightly, you can delete the old Insightly account to stop the billing. Once you upgrade the new account, a new subscription will be billed, but we'll be happy to transfer your balance to the new subscription.