There is an opened payment that is not attached to any document. We are trying to attach this payment to the invoice, but in Payment > Application there is only greyed out button "Reverse Application"
According to documentation http://download.automation.odin.com/oa/7.1/oapremium/portal/en/billing_providers_guide/75880.htm there has to be an opportunity to attach Debit Memo for document "Payment" using tab "Applications" button "Add New Application". But there is no such button in it.
The button "Apply Document" is missing due to the bug with id #PBA-80747 ("No button "Apply Document" for opened processed payments").
The workaround is to apply the payment from the invoice.