退款回调微信使用的是AEAD_AES_256_GCM加密算法。

//支付数据加密模拟
public static String payNotify() throws NoSuchPaddingException, NoSuchAlgorithmException,
        InvalidAlgorithmParameterException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException {
    //密文数据
    String test = DataDemo.V3_PAY_NOTIFY_JSON;
    //随机串
    String nonce = "xxxxxx";
    //附加数据
    String fj = "";
    Cipher cipher = Cipher.getInstance(WxV3Constant.AES_GCM);
    byte[] aesKey = WxV3Constant.KEY_V3.getBytes();
    SecretKeySpec key = new SecretKeySpec(aesKey, "AES");
    GCMParameterSpec spec = new GCMParameterSpec(128, nonce.getBytes(StandardCharsets.UTF_8));
    cipher.init(Cipher.ENCRYPT_MODE, key, spec);
    cipher.updateAAD(fj.getBytes(StandardCharsets.UTF_8));
    byte[] encrypted = cipher.doFinal(test.getBytes());
    return Base64Util.encode(encrypted);
}

//退款数据加密模拟
public static String refundNotify() throws NoSuchPaddingException, NoSuchAlgorithmException,
        InvalidAlgorithmParameterException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException {
    //密文数据
    String test = DataDemo.V3_REFUND_JSON;
    //随机串
    String nonce = "xxxxx";
    //附加数据
    String fj = "";
    Cipher cipher = Cipher.getInstance(WxV3Constant.AES_GCM);
    byte[] aesKey = WxV3Constant.KEY_V3.getBytes();
    SecretKeySpec key = new SecretKeySpec(aesKey, "AES");
    GCMParameterSpec spec = new GCMParameterSpec(128, nonce.getBytes(StandardCharsets.UTF_8));
    cipher.init(Cipher.ENCRYPT_MODE, key, spec);
    cipher.updateAAD(fj.getBytes(StandardCharsets.UTF_8));
    byte[] encrypted = cipher.doFinal(test.getBytes());
    return Base64Util.encode(encrypted);

}

public static void main(String[] args) throws NoSuchPaddingException, InvalidKeyException,
        NoSuchAlgorithmException, IllegalBlockSizeException, BadPaddingException,
        InvalidAlgorithmParameterException {
    String s = payNotify();
    System.out.println(s);
    String s1 = refundNotify();
    System.out.println(s1);

}

你管怎么加密的干嘛，你验证签名没问题就可以进行解密了啊，调试要真实数据请求