I have embedded an website inside another website using iframe.. <iframe src=..">.. Inside the embedded website there is a copy button. When I use it in website(without embed) it works. But when I use it in iframe it doesn't..

My button code: <button onclick="copy()">copy</button> Js:

function copy() {
  let copyText = document.getElementById("resu");
  
  copyText.select(); 
  copyText.setSelectionRange(0, 99999); /* For mobile devices */

  navigator.clipboard.writeText(copyText.value.replace(/A  /, "A ")).then(function() {
  alert("Copied to clipboard.");
}, function(err) {
  alert("Could not copy text.");
});
  }

What's wrong??