If you are not using Classes in QuickBooks Online, then you can skip this section as it is not required.
The “Class” segment on the System > Setup Tables > GL Accounts table in Manage must be consistent with the “Name” field on the Company > Lists > All List > Classes screen in QuickBooks Online. This is applicable per each transaction line of each invoice.
You can map to sub-classes in QuickBooks Online simply by delimiting the Class in Manage with a colon “:”. QuickBooks Online supports sub-classes up to 5 levels deep. An account 5 levels deep in Manage would then be in the format “level1:level2:level3:level4:level5”.
It is important to note that any time that you make changes to your classes and subclasses you need to open save and then close and save any closed invoices that use that mapping for it to change. Once you have done that you can then successfully run the batch in QBO to show the new class. More on this here.