一旦我只填写金额，应该如何打开payu页面？

Question

      $hash         = '';
      $hashSequence = "key|txnid|amount|udf1|udf2|udf3|udf4|udf5|udf6|udf7|udf8|udf9|udf10";

      if(empty($posted['hash']) && sizeof($posted) > 0) {
        if(
              empty($posted['key'])
              || empty($posted['txnid'])
              || empty($posted['amount'])
              || empty($posted['surl'])
              || empty($posted['furl'])
    )

SORRY！         我们无法处理您的付款

    Error Reason
    One or more mandatory parameters are missing in the transaction request.
    The parameters which you have actually sent in the transaction are: 
key, txnid, amount, surl, hash.

Mandatory parameter missing from your transaction request are: 
productinfo, firstname, email, phone.

所以可以链接payu页面只填写金额