I don’t think you have the syntax quite right there. See here for some closer. However, that isn’t working as intended yet because…
More importantly for now though is why did you pick that snapshot from 2019-2-18? I’m looking at the list pf snapshots and when I click on that one, it seems to say it is R 3.5.2 here? Which version of R are you seeking?
I am still getting 3.6.3 currently but it may be because that snapshot date and the 3.6 don’t match?