How to specify the config.http.locations.download parameter to enable r_download?

Hi, on my own local SWISH platform, I am trying to use r_download to download the image rendered by R. However, there is an ‘undefined’ in the file path which should be ‘download’ instead.

After some debugging, I think it is because config.http.locations.download wasn’t specified. Is there a way to specify this parameter? I couldn’t find any documentation for this config.

Many thanks.