To listen to observables use on for one observable or orany for multiple
onany(StartDate, EndDate) do start_date, end_date
xlims!(Price_ax, start_date, end_date)
end
This is now listening for when the observable changes, and then passing the values into xlims with either of StartDate or EndDate changes, and you should see there are listeners for both observables.
Also if you use backticks around code in discourse posts its much easier to read! See