You can activate or delete an inactive bank account in the Manage Bank Accounts app. You cannot revert to active or close an inactive bank account. Reference: Manage Bank Accounts

When an invoice is posted, but no relevant purchase order is available, you need to perform the goods and invoice receipts reconciliation process. This process is used to identify and resolve discrepancies between goods receipts and invoice receipts for purchase orders that are not subject to invoice verification. For example, this can happen when you receive an invoice from a supplier before you receive or record the goods receipt, or when you receive an invoice for a purchase order that was created without reference to a contract or outline agreement. You can use the Goods and Invoice Receipts Reconciliation app to view and clear the discrepancies.