PHP如何将btc转换为usd

Question

我想用PHP制作一个函数，将比特币转换为usd，这是我的代码：

<?php
    function usd2btc($btc) {
      $options = array(
        CURLOPT_RETURNTRANSFER => true,    
        CURLOPT_HEADER         => false,   
        CURLOPT_FOLLOWLOCATION => true,     
        CURLOPT_ENCODING       => "",      
        CURLOPT_USERAGENT      => "spider", 
        CURLOPT_AUTOREFERER    => true,    
        CURLOPT_CONNECTTIMEOUT => 120,    
        CURLOPT_TIMEOUT        => 120,     
        CURLOPT_MAXREDIRS      => 2,      
        CURLOPT_SSL_VERIFYPEER => false   
      );

      $ch      = curl_init( "https://api.coingate.com/v2/rates/merchant/BTC/USD" ); //BTC2USD exange
      curl_setopt_array( $ch, $options );
      $content = curl_exec( $ch ); // Gets the page's content
      $err     = curl_errno( $ch ); // Gets the CURL error number if there is error
      $errmsg  = curl_error( $ch ); // Gets the CURL error text if there is error
      curl_close( $ch );




 if ($btc !== 0) {             
   return round($btc/$content, 2);         
 } else {            
   return 0.00;           
 }      
}

?>

例如，当我运行函数时：

<p>0.002฿ = <?php htmlspecialchars(usd2btc(0.002)); ?>$</p>

它不返回任何东西，甚至不返回0。你们有一些解决方案吗？帮助。