In order for NSX-T to run properly, we need to first create a distributed switch in vCenter and add to it, the esxi hosts. From VMware: NSX Virtual Switch is based on vSphere distributed switches (VDSs), which provide uplinks for host connectivity to the top-of-rack (ToR) physical switches.
Add a distributed switch in vCenter
Add the ESXi hosts to the Distributed Switch
It will take a couple minutes to add the vds to all the hosts and configure them. Once everything is added, you are ready for the next step.