Hello and Welcome. My name is Michael.
I hate to be the one to let you know that the AF-S Nikkor 70-300 VR Lens (Nikon product number: 2161) is NOT compatible with the TC-20EIII.
Here is a link from Nikon showing the only compatible units with the TC-20eIII.
If there is anything else I can help you with on this matter, be sure to let me know.