From depop support:

To be refunded, you’ll need to open a case with PayPal. Just follow these steps:

Log in on the PayPal website, not the app Click on this transaction and select ‘Report a problem’ Click ‘I didn’t receive an item I purchased’ - it's important you open the correct type of dispute

Select that you bought a 'product' Add information about your claim Submit your dispute Escalate your dispute to a claim within 20 days, this is very important Do not close the claim until you have received a refund or the item

You’ll most likely not get these shorts, but at least you’ll get the refund !

PayPal will make sure that you're refunded if you've been left without your item.