I tried the diversity-alpha-rarefaction function, and it worked fine only the image generated could not be downloaded. Additionally, when I passed the metadata file in the command line, the rarefaction curves were collapsed automatically without showing variations for each subsampling point on the image generated and the option for showing individual rarefaction curve was gone. To me, I prefer to show individual rarefaction curve with different colors standing for different experimental conditions. Anyway, this can be done by the users themselves by downloading the CSV files.