e-Invoice Trial web-site is released in http://einvoice1-trial.nic.in. Bulk upload facility can be used here for IRN generation
e-Invoicing System for sandbox API interface (for testing) has been released on portal https://einv-apisandbox.nic.in
  The taxpayer with aggregate turnover of Rs.500 Cr. and above during last financial year can register and test the APIs. Bulk IRN generation facility will also be released shortly