Activation unlock request denied three times despite providing adequate information.

The receipt has to be the original one from Apple or an Apple authorized retailer. Keep your receipt after you buy an Apple device - Apple Support

Ask the seller for a refund or to do the things in this article (some can be done remotely) --> What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support If they won't then you have been scammed. See if eBay has any recourse for you. Selling stolen phones on eBay is pretty common and it is pretty much impossible to tell in advance if the lock has been removed.

Bodhi7507 wrote:

Purchased an iPhone 8 off eBay

Mistake #1

can’t contact seller due to me being lazy

Mistake #2

picture of the invoice from the seller

Needs to be your original purchase receipt from Apple or Authorized Apple seller. Nothing else is acceptable

What you experienced is just 1 of the problems you can encounter whenever you purchase a device from an unknown seller. That was a poor decision. Review this Support Article for more information:

The All Too Common SAD Reality of Buying … - Apple Community

If you have found a device, turn it on and see if there's a message. The owner may have done this:

Use the Find My app to locate a missing device or item - Find your lost Apple device or AirTag with Find My - Apple Support

"What happens if you activate Mark As Lost

...You can also display a custom message with your phone number on the Lock screen, and keep track of your device's location."

For some iPhones see the support article "Return a lost, locked iPhone"; click here --> Return a lost, locked iPhone - Apple Support

Otherwise turn it into authorities responsible for dealing with lost items.

With activation lock ("locked to owner") set you won't be able to use it yourself.