A deferred income is a current liability on the balance sheet. It remains unearned until goods and services are fulfilled and recognised in the sales revenue account.

You do not need a lengthy paragraph explaining why you pay or receive; you need concise information of what and where to explain the why.

Are advance payment, deposit, and prepayment any different?

QuickBooks Online does not have a salesperson field by default; however, you can create one.

Instead of having a job feature like QuickBooks Desktop, QuickBooks Online uses projects and sub-customers. Are they the same?

The account type can be a current assets account, and the detail type uses allowance for bad debts, which is available in QuickBooks Online (QBO).