Extracting "World Reference Base (2006) Soil Groups" data in R and searching for the legend of the extracted values

I downloaded the "World Reference Base (2006) Soil Groups" data per the SoilGrid website as tile1 and processed the data in R (xmin = -116, xmax = -114, ymin = 30, ymax = 32):

### Soil properties of the localities
soil = raster("C:/Users/Besitzer/Documents/MEP/data/soil/tile1.tif")
example_Test@data$soil = raster::extract(soil, example_Test)

I obtained the following values (> example_Test):

[1] NA NA NA NA NA NA NA NA NA 24 NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA
[37] NA NA NA NA 24 NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA  4 NA NA NA NA NA 24  4 NA 24 24  4 NA NA NA NA

I expected values like: HS or AT or TC. Where do I find a key on how to interpret the extracted numbers? –> 4, 24, see above