i was using:
Mono JIT compiler version 4.6.2 (Debian 4.6.2.7+dfsg-1ubuntu1)
but i had to go through the process of purging mono stuffs and installing the stable mono repo to get duplicati to work with box.com. now i have:
Mono JIT compiler version 6.0.0.313 (tarball Sun Jul 14 09:57:59 UTC 2019)
https://github.com/duplicati/duplicati/issues/3767#issuecomment-517525034