Callbacks

General Information

• Represents an HTTP POST request to the client's system at a URL configured in the personal account
• Data in the request and response body is available in JSON format
• The request contains headers:
  • Content-Type: application/json
  • User-Agent: information about the calling system
• Dates are transmitted in UTC in ISO 8601 format. For example: 2024-07-02T12:50:30Z

Callback URL Requirements

1. Use secure HTTPS protocol
2. Use domain names, not IP addresses

Authentication

Authentication for callbacks is performed by sending headers in the request, similar to the headers for API request authorization (see Authorization section).

Callback Verification

To avoid fraud, the client's system must verify the specified callback header values as follows:

1. The difference between the current server time and the X-Processing-Timestamp header value does not exceed the X-Processing-RecvWindow header value
2. The X-Processing-Key header value matches the value of the client's active public API access key
3. The X-Processing-Signature header value matches the signature of the request data with the secret key

Callback Handling

Successful Response

If the callback request is successful, the client's system must respond with HTTP code 200 OK.

Idempotency

If after a successful response to a callback request, a similar request arrives again, it is necessary to generate the same response as for the previous one.

Requests are considered similar if they have identical values for the following parameters in the request body:

• type - Transaction type
• id - Transaction identifier in the processing system
• status - Transaction status

Transaction Uniqueness

To determine whether multiple callbacks relate to one transaction or different ones, use the combination of type and id parameters from the root element in the callback JSON. This combination is unique for all transactions.

Retry Policy

Non-Retry Codes

The callback will not be retried when receiving a response from the client's system with the following HTTP codes:

• 1xx
• 3xx
• 4xx

Retry Codes

In case of a response with HTTP code 5xx, the callback remains in the send queue and send attempts continue according to an exponential backoff policy.

Backoff calculation formula:

60 seconds + {number of retries}^4

Maximum number of retry attempts: 10

Retry Intervals

Attempt	Interval	Total Time
1	61 sec	61 sec
2	76 sec	137 sec
3	141 sec	278 sec
4	361 sec	594 sec
5	685 sec	1,279 sec
6	1,356 sec	2,635 sec
7	2,461 sec	5,096 sec
8	4,156 sec	9,252 sec
9	6,621 sec	15,873 sec
10	10,060 sec	25,933 sec (~7.2 hours)