Undeposited Funds are payments that you've received but haven't yet deposited. For Amazon, this includes all of your current sales income. This type of account is also known as a clearing account or a holding account.
You'll have to create a new Bank account with Detail Type Cash on hand or Checking in QuickBooks Online. Name it Amazon US Undeposited Funds or something similarly descriptive. Then click on the refresh button and select it on SellerZen.
This option allows you to choose the account to deposit sales income from your current settlement period.
Once Amazon disburses your current settlement, the amount from this account will be transferred to your selected disbursement account under the Settlement tab.
The balances between the account you choose for this field and your current Amazon settlement will be approximately the same. This is because of pending transactions.