Hi,
If you have created a Item based AP Invoice, then check in the Item master Data by which 'Items Managed by' is taken under the Inventory Tab.
If Item, then check the G\L Accounts in the matrix row of the Warehouse in same tab.
If Warehouse, then check the warehouse defined for the Item and check the Accounting Tab of the that Warehouse.
If Item Group, then check the Item Group to which the Item assigned and again the accounting tab of that Item Group.
Kind Regards,
Jitin
SAP Business One Forum Team