question on shipping credit on ebay

[Dznypal]

Usually when I sell something on ebay and I print the shipping label

theres usually a credit for the shipping

on the item I just recently sold when I printed the label there wasn't a discount

I looked under customer support but when I checked it said some items have requirements for the discounts

when I clicked to see what the requirements were it says "view details of items that sold"

that doesn't tell me what the requirements are

any ideas

thanks all