You should not have to pay unless weight and size exceeds the amount of both which are allowed on the label. So long as you are returning the item on the same packaging as you received it in. That's an eBay policy. The weight is usually printed on the label.
It should say if the label is pre paid or just a label with address for accurate returns. Look for a bar code. I am more familiar with Amazon returns which are prepaid by Amazon. I hope you get it sorted out. :)
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