I created a pie after the marked closed and canceled the pending auto-invest (investing at opening time is stupid).
When I now click “invest”, it recognizes the 200 CHF cash and even says it will use it, but then claims that there is insufficient funds. The slider is disabled but you can enter a number.
EDIT: What it is probably telling me is that I do not have 200 CHF free funds available additional to the cash already in the pie. It works when adding funds to have at least 20$. But err, it does not feel intuitive to me.