$curls = array(
CURLOPT_HEADER => 0,
CURLOPT_FOLLOWLOCATION => 1,
CURLOPT_AUTOREFERER => 1,
CURLOPT_RETURNTRANSFER => 1,
CURLOPT_CONNECTTIMEOUT => 15,
CURLOPT_TIMEOUT => 15,
CURLOPT_VERBOSE => 0,
CURLOPT_SSL_VERIFYHOST => 0,
CURLOPT_SSL_VERIFYPEER => 0
);
function Return_URL($url){
global $curls;
$ch = curl_init();
curl_setopt_array($ch, $curls);
curl_setopt($ch, CURLOPT_USERAGENT, "Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/89.0.4389.128 Safari/537.36"); //Tarayıcı sürümü
curl_setopt($ch, CURLOPT_URL,$url);
$html= curl_exec($ch);
curl_close($ch);
return $html;
}
function getir($ilk, $son, $yaz) {
    @preg_match_all('/' . preg_quote($ilk, '/') .
    '(.*?)'. preg_quote($son, '/').'/i', $yaz, $m);
    return @$m[1];
}
function cevir($from,$to,$amount) {
    $url = Return_URL("https://www.forbes.com/advisor/money-transfer/currency-converter/".mb_strtolower($from)."-".mb_strtolower($to)."/");
    $rate = getir('"latestRate":"', '"', $url);
    // $exchange_rate = $rate[0]+0.15;
    $convertedAmount = $amount*$rate[0];
    $amount_convert = number_format($convertedAmount, 4, '.', ',');
    return $amount_convert;
}
echo cevir("USD", "TRY", 1); // sonuç: 1 Dolar = 19.82 TL

Yukarıdaki fonksiyonu dilediğiniz gibi projelerinizde veya kur çevirmek istediğiniz bölümlerde kullanabilirsiniz.

Kaynak: https://www.r10.net/php/3684183