---
title: "Calls and callbacks"
url: "https://docs.adyen.com/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/calls-and-callbacks-c-library"
source_url: "https://docs.adyen.com/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/calls-and-callbacks-c-library.md"
canonical: "https://docs.adyen.com/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/calls-and-callbacks-c-library"
last_modified: "2026-05-24T12:54:31+02:00"
language: "en"
---

# Calls and callbacks

[View source](/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/calls-and-callbacks-c-library.md)

The library handles function calls asynchronously. The system returns results in the form of callbacks. All calls to the library are non-blocking.

Calls will return a result to say whether or not they were accepted. You provide a callback function in the call. If a call is accepted, you will receive a response in the user-provided callback function. You must write functions to handle the response.

Because the library processes asynchronously, and callbacks are required to get additional info from the attendant, a number of callback routines must be specified. The library returns these callbacks to the above calls whenever additional input is required.

These callbacks are asynchronous responses to a synchronous call:

1. [Library initialization callback](/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/key-steps-c-library/initialize-the-library-c-library)
2. [Register POS callback](/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/key-steps-c-library/register-the-application-with-adyen-c-library)
3. [Register PED callback](/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/key-steps-c-library/register-the-ped-with-the-adyen-payments-platform-c-library)
4. [Create tender callback](/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/key-steps-c-library/process-a-basic-transaction-c-library/create-the-tender-c-library)
5. [Cancel or Refund callback](/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/key-steps-c-library/cancel-or-refund-a-transaction-c-library/cancel-a-transaction-c)
6. [Show Screen callback](/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/extras-c-library/display-a-screen-on-a-large-screen-terminal-c)
7. [TxStoreReport callback](/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/extras-c-library/get-transaction-data-from-tx_store_report-c)
8. [Library exit callback](/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/key-steps-c-library/exit-the-library-c-library)

These callbacks are related to transactions, and will require actions to be performed:

1. [Receipt callback](/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/key-steps-c-library/process-a-basic-transaction-c-library/handle-the-print-receipt-callback-c-library)
2. [Signature callback](/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/key-steps-c-library/process-a-basic-transaction-c-library/handle-the-signature-callback-c-library)
3. [Additional data callback](/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/key-steps-c-library/process-a-basic-transaction-c-library/handle-the-additional-data-callback-c-library) 

These callbacks are related to transactions, and will require no actions to be performed:

1. [Progress event callback](/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/key-steps-c-library/process-a-basic-transaction-c-library/handle-progress-events-c-library)
2. [Dynamic Currency Conversion callback](/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/extras-c-library/handle-dynamic-currency-conversion-c-library)
3. [Final result callback](/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/key-steps-c-library/process-a-basic-transaction-c-library/handle-the-final-state-callback-c-library)
4. [PED State callback](/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/key-steps-c-library/process-a-basic-transaction-c-library/handle-the-ped-state-change-callback-c-library)