# Introduction **Background** The GST Council has approved the implementation of ‘e-Invoicing’ or ‘electronic invoicing’ in a phased manner for reporting of Business to Business (B2B) invoices to GST System, starting from 1st January 2020 on a voluntary basis. Being the first Invoice Registration Portal (IRP), National Informatics Centre, has made the e-Invoice registration services available through API mode, in addition to other modes. The tax payers and GSPs can integrate their business systems and processes with the e-Invoice system through these APIs for seamless registration of the invoices, generated/prepared on their systems. **Purpose of this portal** This portal enables/provides: * Developers or System integrators of the taxpayers to understand the interfacing processes of e-Invoicing system with their business systems. * Registration of the users to access the APIs * **Credentials:** The portal explains how to get the credentials to access the APIs on **sandbox and production environments.** The credentials include **client-id, client-secret, username and password.** * API Documentation * This portal provides all the information required by the application developers related to integrating their systems with the e-invoice system through APIs. * This includes the calling methods / URLs, JSON Schema of the request payloads, sample request payloads and sample responses, validations being applied, etc., for each of the APIs. * Sample code extracts, for reference, are provided for understanding the logic and concepts. * Other references like the master data used in the system etc. are provided. * Understanding / Testing the API methods through the sandbox portal. Through this portal, the developers can simulate the use of APIs, end-to-end. * Can understand how the request payloads can be generated. * Can see how the encryption and decryption of the requests and responses work. * Can substitute the encrypted payload generated using his/her system and check for the correctness of encryption * By changing the parameter values in the request payloads, developers can test the successful (valid) and unsuccessful (invalid) responses for different combinations of values. * What will be the response if any of the credentials supplied are wrong? * What will be the error response when any of the mandatory parameters are missing in the payload? * What types of errors are displayed when the API fails? * What happens if the API is called without a valid token? --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.mastersindia.co/einvoicing/introduction.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.