Multiple modes are available so taxpayers can use the best mode to generate IRN: 

• API-based
• Offline Utility (freely downloadable from IRP) Web-based / mobile app-based modes will also be provided in future. 

1. API-based integration modes are as follows: 

Taxpayers with Aggregate Turnover of < Rs. 500 Crores:

• Through E-Way Bill APIs: If the taxpayer already has direct access to E-Way Bill APIs, they can use the same Client Id, Client Secret, username, and password to access the e-Invoice system. 
• Through GSPs: the taxpayer can connect through GSPs. In this case, the GSTIN generates their username and password and ties up with GSPs to access e-invoice APIs using the Client ID and Client Secret of GSPs.
• Through ERPs or Billing/Accounting Software Service Providers: the taxpayer can connect through select ERPs and Billing/Accounting Software Service Providers. In this case, the GSTIN generates their username and password and ties up with ERPs or Billing/Accounting Software Service Providers to access e-invoice APIs, using the Client ID and Client Secret of said providers.
• Through Entities having direct Access to APIs: If the taxpayer (e.g. certain automobile companies) has tied up or used the ERP of the entity which has direct access to API, they can access e-invoice APIs through that entity. In this case, the GSTIN generates their username and password and access e-invoice APIs, using a Client ID and Client Secret of the entity with such access. Taxpayers with Aggregate Turnover of > Rs. 500 Crores: In addition to the above modes, they will have direct access, as follows: 
• Direct Access to API: They can get direct access to API to integrate with their ERP system. They need to whitelist their public IPs. In addition to the username and password to each GSTIN of the entity, the entity gets the Client ID and Client Secret to get access to e-invoice APIs.

B. Through Offline Utility: Some businesses may not have their own ERP/Accounting Software or have few invoices to report. They can download the free offline utility (‘bulk generation tool’) from the e-invoice portal. Using this can easily upload invoice data on IRP to generate IRN. While the portal gives back ‘machine-readable’ invoices in JSON format, there is a facility to generate a ‘human-readable’ PDF copy of the invoice (for save/print/e-mail etc.).