Zonal Statistics in QGIS 3.16

I have a NDVI raster file generate from Landsat-8 data and using the Identify Features tool I am able to observe the individual values per pixel. I also have a vector kml file breaking down a region into a number of areas. I am trying to use zonal statistics to gain average, mean etc from the raster data for each area of the vector file. However, when I complete the zonal statistics all the calculated values are null.

Any ideas as to what I might be doing wrong?