Error: extend volume size is not supported

Hi please help me

This is the issue

My D drive is shared one is showing 13 giga free on 300 Go

but all my files when i right click on them are 200 Go

so the D drive is showing full , normally i have 100 Go left inside.

When i go to server manager i see that the D shared drive is 200 (instead of 300 Go)

I try to right click extend and extend the volume

i see: actual size: 200 / maximum size: 300

new size i tryed 299 but its said error when clicking ok " size is not supported"

why i dont have the 300 Go on the server manager disk volume?

how i can add those 100 giga?

why the D drive is showing 300? and not using 300? but only 200?

please help thanks