"The final installment of sales order '%1' can only be closed when all cost prices are known." Why do you receive this message and what can you do to resolve it?

"Sales order '%1', line '%2' is historical and contains installments. Returns are not possible." Why do you receive this notification and what can you do to resolve it?

What can you do if a closing invoice is not a zero invoice and the sales order lines can no longer be assigned?