eBay has been informing every member (buyer and/or seller) about Managed Payments for years – well before it was implemented. As a buyer only, I was informed. I still have the emails.

You cannot possibly claim that you have never heard of Managed Payments unless you ignore all communication from eBay and haven’t ever checked the Seller Hub. That would mean you have a laissez-faire approach and don’t keep yourself informed of the necessary changes to T&Cs. Everything has changed … I strongly suggest you read the eBay Help pages on selling (esp the one titled “Registering as a seller”) as a matter of urgency. Under MP (and as a result of the current anti-money-laundering laws affecting fee disbursement in Australia), you are now regarded as a new seller and you MUST be registered for MP and verified with both your ID and your bank account.

Refunding

❝Here's how to issue a refund:

1. Locate the order in Seller Hub or My eBay Sold.
2. From the drop-down menu, select Send refund.
3. Choose a reason for the refund.
4. Specify a refund amount for the item or for the order.
5. Enter the desired refund amount, and select Send refund.

You'll get an email confirming that the refund has been initiated, and another email once the refund is complete. The refunded amount will appear in your order details. You can refund up to 100% of the transaction.

If you're issuing a partial refund for an order, the amount will be split proportionally across each item in the order.❞

— https://www.ebay.com.au/help/selling/managing-returns-refunds/refunding-buyers?id=5182