The callback is used to asynchronously notify the merchant about changes to the recurring profile status. When creating a recurring profile, the merchant provides a callback URL. After the payer follows the provided link and signs the agreement, the recurring profile status changes, and the system sends a notification to the specified URL. The callback on the merchant side must be public, without authorization.Response and Retry Policy Merchant must return HTTP 200 OK to acknowledge successful receipt of the callback. The response body is not required and will be ignored. 200 OK - the callback has been received and acknowledged by the Merchant. No further retries will be performed. If no HTTP 200 OK response is received, the system considers the callback delivery unsuccessful and will retry the invoice state callback once every 30 seconds.A maximum of 3 retry attempts will be performed. If all 3 retry attempts fail, the callback delivery is considered unsuccessful. The following cases are considered a failed delivery: connection timeout; connection refused; network error; any HTTP response other than 200 OK; no response from the Merchant. The Merchant is not required to return a specific HTTP status code for a business-level processing error. The callback is considered successfully delivered only when HTTP 200 OK is returned.