No, you can't just use your $25 gift card directly. You must first link either a bank account or a credit card to your PayPal account.
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You can use an eBay gift card or gift certificate to pay for all or part of a purchase. After clicking Pay Now to pay for the item, you'll be prompted to enter your redemption code.
If you're having problems using a gift card or gift certificate, here are a few things to check:
The seller must accept PayPal for payment.
You must have a PayPal account. If you don't already have a PayPal account, you'll be given an opportunity to sign up.
Your eBay email address must be listed on your PayPal account. If it isn't, you can add your eBay email address by updating your PayPal profile.
Your PayPal account must have a bank account or credit card associated with it. This account information is required for security purposes.
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eBay Customer Support