We would like to have an authenticity verification page, where customers enter a unique code.

Hi Tushar,

You can create a collection with fields: Product Name, Serial Key… blah blah blah

Then, you can use have an input for the user to enter the Serial Key, and a button to call the code.

Code:
When the user clicks the button, the code looks for the data
(https://www.wix.com/velo/reference/wix-data/query)

wixData.query("myCollection")
.eq('key', $w('#keyInput'))
  .find()
  .then( (results) => {
    if(results.items.length > 0) {
      // tell user the item exsits! :)
      $w('#have').show() //this should be your tick image
      $w('#fake').hide() //this should be your cross image
    } else {
      // It is fake! We don't have this key! :(
            $w('#have').hide() //this should be your tick image
      $w('#fake').show() //this should be your cross image
    }
  } )
  .catch( (err) => {
    let errorMsg = err;
  } );