@MUHAMMAD MUBUSHER ASLAM don’t let Netsuite’s terminology confuse the situation. What they call Token-based Authentication is really just OAuth 1.0 (with realm being required). You can use any OAuth 1.0 compatible client or library to achieve the integration. But, note that NLAuth and OAuth 1.0 are mutually exclusive. Both of them are written to the Authorization header, so you can only use one method of authentication. You must eliminate or remove anything related to the custom NLAuth header in order for OAuth to work.

Sorry, you are right it was nlauth_otp

As of 2021.1, you HAVE to use Oauth 1/2