To enable publishing to FLEX, you will need the 7.2.1 or newer version of the add-in. There is also a settting on Admin-Company-Projects to enable each project to be published to FLEX. Only Revit models are currently supported on Flex.
This initial rollout includes tracking status and package filters. We are working on performance optimizations, particularly for larger models. Additional features will be continuously added in future releases, further refining the model viewer's functionality and user experience.