AP Account
The AP Account field is required and will default to the Accounts Payable account based on the rules specified on the System Default -- Posting Group.
Depending on the Account Source Type field (designated on the System Default Posting Group), the account will be defaulted as follows:
A default value may or may not be defined. Users with AP User or AP Poster roles can override the provided default value. The list of available accounts that can be selected from will include all active accounts that allow transactions and have an Account Type of Liability (as defined on the Admin >> Setup >> Accounts screen).