Once the last two steps are successfully completed. That is - the user has enabled API access on his GST Portal and GenerateOtp API an OTP has been sent. Then, this API is used to verify the OTP and enable access to GST Portal.
This API will start a session and provide access valid for 6 hrs. Returns date timestamp of the expiry of the session.
The end result of Tax Payer authentication process is to establish an authorization token for the session which needs to be included in the header for all subsequent API calls.