Transactions > Customers > Issue Customer Refund: Check # field is grayed out.

The Check # field on Customer Refund > Refund Method tab is grayed out by system design if the Refund Method selected is a credit card type. 

To verify this information:

1. Navigate to Setup > Accounting > Accounting Lists.

2. Set Type = Payment Method.

3. Edit/View the Payment Method used for the Customer Refund.

4. Verify if Credit Card checkbox is enabled.