In general auto-focus modules don't work too well if the maximum aperture (effective) is greater than f5.6. The 70-300VR is an f4-5.6 lens so adding a 1.4X TC would make it f5.6-8 and your camera would struggle to autofocus.
I once had a 80-400VR f4.5-5.6 where all Nikon TC's were incompatible but the Kenko range did work and maintained VR also, IQ was bad so the idea was scrapped.
I must advise that a TC is only recommended with the finest glass in front. As the TC is spreading the light of the rear element of the primary lens it will exaggerate all imperfections and add its own. I.E. Chromatic Aberration (CA) will no doubt increase and sharpness may decrease.
I have two TC's and they are fine with 70-200VR f2.8 and 300 f2.8, they are not recommended for use with 28-70 f2.8 as the rear element will smash into the TC if used - I don't want that risk!
Hope this helps.
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