It's a scam.
Report the buyer https://www.ebay.com/help/selling/resolving-buyer-issues/reporting-issue-buyer?id=4084 Use the reason "asking to complete a sale off eBay".
Add the buyer to your blocked bidder list: https://www.ebay.com/bmgt/BuyerBlock Ignore any further messages from them.
Cancel the sale immediately using "problem with buyer's address". You don't have to let the unpaid item process play out. They're a scammer - the don't care if they get an unpaid item strike. One account gets soiled and they move on to one of a hundred new ones. You can do that here: https://www.ebay.com/help/selling/getting-paid/cancelling-transaction?id=4136
For your reference, this is how the scam works:
All contact should always be through eBay messages. Do NOT, under any circumstances, give your phone number or email address to a buyer. Do not send a Paypal invoice, either. Your email address can be found on the invoice. Do not click links that claim to fix a buyer's payment issue. There is no legitimate link for buyers to fix a payment issue.
No legitimate buyer needs any of these things, and no legitimate buyer will give up their eBay buyer protection by paying off site. Your "buyer" wants your email or phone number so they can send you a very real looking, but very fake payment email. They are hoping you are too inexperienced to verify the payment. There will be NO PAYMENT, only a fake email saying you've been paid and you must ship immediately so the payment can be released. This is a lie. This person wants you to ship your item without being paid. They want to steal your stuff. Gift cards are just icing on the scam cake.
As long as you are aware of this, you can follow the process above. Bookmark the links for future use. Trust your gut - if it feels wrong, it usually is. If you ever have any questions you can always come here and ask.
Once you build some seller feedback they will leave you alone for the most part. These scammers are a pain, and there is no real way for eBay to stop them until after the fact. The majority of them are overseas using VPN, and when one account gets shut down, 100 more will take its place, either using new accounts or hacked old, established accounts. They target new sellers, hoping to cash in on their inexperience and lack of knowledge of the scam.
The easier you are to offend the easier you are to control.
We seem to be getting closer and closer to a situation where nobody is responsible for what they did but we are all responsible for what somebody else did. - Thomas Sowell
