“but can I do the same for the sales, material costs and expense?”

The additional piece of info that is Class, is assigned to everything detail you enter at the bottom of the Check, credit card  charge, bills, invoices, sales receipts, on these detail lines.

“Intuit grabbed on to this question and […]

Resolution for '2 sales accounts issue: 'Can I create 2 sales accounts and 2 material cost accounts within one company file?' available: Yes.

The 2 sales accounts 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 2 sales accounts issue yourself by looking for a resolution described in the article. If it is a complex 2 sales accounts issue or you are unable to solve the issue, you may contact us by clicking here or by using other 2 sales accounts support options.

For more information about resolving issues related to 2 sales accounts in Quickbooks/QBO or to get support for the issue 'Can I create 2 sales accounts and 2 material cost accounts within one company file?', click the link below: