As of the 2020.1 release of NetSuite, sessions may no longer be established with the API via a Login / Logout request. This has made the connection property UseSessions obsolete, so we have had to remove it. This has been a part of NetSuite changes that have enforced individual integrations to be used in order to take advantage of session concurrency. This means that it is no longer possible to use User and Password authentication and along with concurrent requests.

Instead, you must use token based authentication or OAuth moving forward if you would like to take advantage of concurrent requests. If you are currently using user/password, we encourage you to take a look at switching to Using OAuth Authentication. Once you have created an integration in NetSuite, simply set the MaximumConcurrentSessions to match what you have specified for the integration.