Just comment the following line in \lib\Dropbox\RequestUtil.php(line.no : 19)
if (strlen((string) PHP_INT_MAX) < 19) {
// // Looks like we're running on a 32-bit build of PHP. This could cause problems because some of the numbers
// // we use (file sizes, quota, etc) can be larger than 32-bit ints can handle.
throw new \Exception("The Dropbox SDK uses 64-bit integers, but it looks like we're running on a version of PHP that doesn't support 64-bit integers (PHP_INT_MAX=" . ((string) PHP_INT_MAX) . "). Library: \"" . __FILE__ . "\"");
}