Increase receipt amount in Internet Expense Audit Manager

According the documentation, users should be able to change the amount of a receipt line in Internet Expense Audit Manager.  It doesn't say that you can't increase the amount, but when our payables department tries increase an amount, they get an error:

You cannot increase the reimbursable amount. The amount of the expense before the adjustment was: 9.95.Is there a place to change this setting?  We are on R12.Thank you,Catherine