I have a issue. When I send form i get 405 error. I don't understand why. And in console I see 'Error'

My code:

useEffect(() => {
    if (Object.keys(data).length) {
      let xhr = new XMLHttpRequest()
      
      xhr.open('POST', 'https://test-1a68b-default-rtdb.firebaseio.com/', true)
      xhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded')
      xhr.responseType = 'json'
      xhr.send(JSON.stringify(data))

      xhr.onreadystatechange = function () {
        if (xhr.readyState < 4)
          console.log('Loading')
        else if (xhr.readyState === 4) {
          if (xhr.status === 200 && xhr.status < 300)
            console.log('Success')
          else
            console.log('Error')
        }
      }
    }
  }, [data])