It is usually a 10% discount on additional Essentials or Plus subscriptions.
https://community.intuit.com/articles/1145150-creating-a-new-company-or-multiple-companies

Resolution for 'additional Essentials issue: 'Can I get a discount on QuickBooks Online companies if I have more than one under the same QBO account? If so, how much is the discount on Essentials and on Plus?' available: Yes.

The additional Essentials issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the additional Essentials issue yourself by looking for a resolution described in the article. If it is a complex additional Essentials issue or you are unable to solve the issue, you may contact us by clicking here or by using other additional Essentials support options.

For more information about resolving issues related to additional Essentials in Quickbooks/QBO or to get support for the issue 'Can I get a discount on QuickBooks Online companies if I have more than one under the same QBO account? If so, how much is the discount on Essentials and on Plus?', click the link below: