1. API intro

Applicable object: Common mode Institutional mode

Request URL: The URL is set by the parameter notify_url submitted in [Order Placement API] and the https protocol is required. If the URL cannot be accessed, the merchant will not receive any WeChat notifications. The URL must be directly accessible without any parameters. For example: notify_url: http://pay.weixin.qq.com/wxpay/123456789

2. Notification Rules

After the user completes the payment, WeChat will send both the payment result and the user information to the merchant. The merchant needs to receive and process the information, and return the successful response. Notification will only be sent if the payment is successful.

When notifying the interaction to the backend, if the response received by WeChat is unsuccessful or timeout, WeChat considers it as a notification failure and will send it again by following certain strategies to maximize the success rate, but WeChat does not guarantee a successful notification. （Notification frequency:15s/15s/30s/3m/10m/20m/30m/30m/30m/60m/3h/3h/3h/6h/6h - in total 24h4m）

3. Notification Message

For payment result notifications, access the notification URL set up by the merchant with the `POST` method, and the notification data is transmitted through the request body (BODY) in the `JSON` format. The notification data contains the details of the encrypted payment result.

The procedure of how to decrypt the notification data is described as follows.

1、Obtain APIv3 Secret from the merchant platform and record it as key.

2、For the algorithm described in `resource.algorithm` (which is AEAD_AES_256_GCM), obtain the corresponding `parameters nonce` and `associated_data`.

3、Decrypt the `resource.ciphertext` with `key`, `nonce`, and `associated_data` to obtain the resource object in JSON form.

Note

For the information on the API of the algorithm `AEAD_AES_256_GCM`, see rfc5116. The length of the `key` used for WeChat Pay is 32 bytes, the length of the random string `nonce` is 12 bytes, and the length of the `associated_data` is less than 16 bytes or may be zero.

4. Request Parameters

5. Notification Signature

Encryption does not guarantee that the notification request comes from wechat pay. Wechat pay will sign the notification sent to the merchant and put the signature value in the Wechatpay-Signature of Notification's HTTP header. The merchant should verify the signature to confirm that the request is from wechat pay, not other third parties. For the algorithm of signature verification, please refer to 《Wechat Pay API V3 Signature Scheme》。

6. Callback Example

Payment Success Result Notification

{
	"id": "f7c34059-0f2d-5b32-ba33-a42dks0597c5",
	"create_time": "2018-06-08T10:34:56+08:00",
	"resource_type": "encrypt-resource",
	"event_type":"TRANSACTION.SUCCESS",
	"summary": "payment succeeded",
	"resource": {
		"algorithm": "AEAD_AES_256_GCM",
		"ciphertext": "...",
		"associated_data": "",
		"nonce": "..."
	}
}

List of decrypted resource objects:

{
	"id": "1008450740201411110005820873",
	"sp_appid": "wx2421b1c4370ec43b",
	"sp_mchid": "10000100",
	"sub_mchid": "20000100",
	"out_trade_no": "20150806125346",
	"payer": {
		"sp_openid": "oUpF8uN95-Ptaags6E_roPHg7AG0"
	},
	"amount": {
		"total": 528800,
		"currency": "HKD",
		"payer_total": 518799,
		"payer_currency": "CNY",
		"exchange_rate": {
			"type": "SETTLEMENT_RATE",
			"rate": 8000000
		}
	},
	"trade_type": "MICROPAY",
	"trade_state": "SUCCESS",
	"trade_state_desc": "Payment successful",
	"bank_type": "CCB_DEBIT",
	"attach": "Payment test",
	"success_time": "2018-06-08T10:34:56+08:00",
	"promotion_detail": [{
		"promotion_id": "109519",
		"name": "Single-item discount-6",
		"scope": "SINGLE",
		"type": "DISCOUNT",
		"amount": 1,
		"currency": "HKD",
		"activity_id": "931386",
		"wechatpay_contribute_amount": 1,
		"merchant_contribute_amount": 0,
		"other_contribute_amount": 0,
		"goods_detail": [{
			"goods_id": "iphone6s_16G",
			"goods_remark": "Product remarks",
			"quantity": 1,
			"price": 528800
		}]
	}]
}

7. List of decrypted resource objects

8. Response Result

Response for successful request: The HTTP response status code needs to return 200 or 204, there's no need to return the response message.

Response for failed request:The HTTP response status code needs to return 5XX or 4XX, the response message needs to be returned.

The format is as follows:

200
{
	"code": "SUCCESS",
	"message": "OK"
}
    

{
    "code": "SYSTEM_ERROR",
    "message": "ERROR"
}