If you create a group in the Chart of Accounts and call it the typical “Cash & Cash equivalents” then you can list bank, cash and any other account such as Amazon. In Manager you create the Amazon Account similar to a normal bank account, including a control account. This is perfectly legitimate and is the right way to use 3rd party accounts.
No, it is not. As @eko explained, this transaction represents money coming into the business, so a journal entry should not be used.
My original comment was directed only to your choice of account and your complaint that your inventory was not updated. It was not updated because no inventory-related account was included in the journal entry.
A sale of inventory involves many accounts:
Inventory on hand is credited
Inventory - cost is debited
Inventory - sales is credited
A cash or bank account is debited (assuming a non-credit sale)
Accounts receivable is debited (assuming a credit sale)
When used correctly, Manager accomplishes all of these for you. You included only one of four necessary lines in your journal entry and introduced your erroneously defined Amazon Account.