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”.