You have agreed to this, when signing up as an eBay seller. You need to sign up for eBay's Managed Payments to be able to sell on eBay, see here:
You need to provide eBay with details of a bank account and have this account verified. The usual method here, is for eBay to send 2 micro deposits into that nominated bank account for you to receive, and confirm to eBay.
Once this is completed, you will be able to list items for sale, and receive payouts from those sales.
This will show you how to register for eBay's Managed Payments.
https://www.ebay.co.uk/help/help/selling/getting-paid/introducing-managed-payments-ebay?id=4795
Should any refunds be necessary in the future, and there is no money instantly available in your eBay Balance, then eBay use your back up source which is usually your bank account.
Money from the sale is placed on hold, and once the refund is finalised, that money is released to you.
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