Transactions you canceled for being out of stock

[olivershoping]

I have worry about this cancelation, I have only two variation shoes 8 and 8.5 two week ago I sold the number 8.5.

New costumer buy 8.5 the size I ready sold. Them I call text to the costumer and ask do you buy 8.5 he say yes.

so I don't have that size, my inventory only have 8 because 8.5 was sold two week ago. 

Everything was fine we agreed to canceled and refound the money.

My question is how to erase in my deskbord the (Transaction defect rate).  because was not my fault.