You need a subscription per business

IRS Pub 583, Page 5 – must keep separate books per company

and for sole proprietors
IRS Pub 334, page 40 – “If you have more than one business, you must figure your net profit or loss for each business on a separate Schedule C.”
IRS Pub 334, […]

Resolution for 'account multiple issue: 'How to account multiple businesses' available: Yes.

The account multiple 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 account multiple issue yourself by looking for a resolution described in the article. If it is a complex account multiple issue or you are unable to solve the issue, you may contact us by clicking here or by using other account multiple support options.

For more information about resolving issues related to account multiple in Quickbooks/QBO or to get support for the issue 'How to account multiple businesses', click the link below: