Entering a expense as a credit in WIPS

SOLVED

We issued a check several months ago and the expense was entered into TimeSlips through: Time and Expense > Enter an Expense Slip.  The expense entry was invoiced out to the client.  There will be no additional work for this client on this matter.  We now have received that check back and requested to void it.  How do I enter a expense slip as a credit in:  Time and Expense > Enter an Expense Slip.  I can't get it to accept a credit expense slip.  Thank you.