undefined index setting cookie

If I check the "remember me" checkbox and login, the cookie is set as it should be. However, if I don't check it I get a "undefined index" error. I am not sure how to resolve this. The error is for the very first line with the if statement.

if($_POST['remember']=="on"){
						
						$cookie_name = 'userID';
						$value = $safe_userID;
						$expire = time() + 60*60*24*7; 
						$path = '/';
						$domain = NULL;
						$secure = FALSE;
						$httponly = TRUE; 

setcookie($cookie_name, $value, $expire, $path, $domain, $secure, $httponly);

P.S. I am not actually using the auto increment user id, I have another one stored in the database which is created with:

 return strtr(
        base64_encode(
            random_bytes(9)
        ),
        '+/',
        '-_'
    );