Adjustments are generated automatically for paid invoices where the invoice balance was $0, but once again has a balance in the accounting/ERP system
Adjustments occur most commonly when a customer is refunded, the invoice balance was zero but now has a balance again after the refund.
i.e. an invoice was paid but after the customer receives a refund and the payment has been removed the accounting system, it will have a balance again. Armatic will always show whatever the balance reported from the accounting system.