setcookie not working wordpress because of header

Question

I have a WordPress plugin that wants to create cookies but it doesn't work. I would really appreciate a help.

add_shortcode( 'watchlist', 'cwatchlist_short' );
  
function cwatchlist_short() {
	echo '<div class="wrap"><center>';
echo "<form method='POST' action=''";
echo '<p>Please enter the initial of the cryptocurrency or the symbol you want to add to the watchlist!</p> <p>For example: BTC</p>';
	echo "<p><input type='text' name='symbol' placeholder='Initials or symbol'>";
	
	
			echo "<p><input type='submit' value='Submit'>";
			echo "</form></center>";
	echo '</div>';
	if (isset($_POST["symbol"])){
  $x = $_COOKIE['xvalue'] + 1;
setcookie( 'xvalue', $x, time() + 108000, COOKIEPATH, COOKIE_DOMAIN   );

debugging shows: Cannot modify header information - headers already sent by I really need help. Thank you best regards

Answer 1

setcookie function can not work on direct page run process, its always throw header already set error message.
To solve this issue must use new function for setcookie & add this function on init action.

For Ex.

add_action( 'init', 'my_setcookie_example' );
function my_setcookie_example() {
	setcookie( "name", "value", time(), "/", COOKIE_DOMAIN );
}

In Your case,need to remove "setcookie( 'xvalue', $x, time() + 108000, COOKIEPATH, COOKIE_DOMAIN );" & place into function, After that add "add_action" hook on place of it.