Plotting markers of one dataset onto another trace value

Hi,

I have 2 data frames:
df1 contains columns: “time”, “bid_price”
df2 contains columns: “time”, “flag”

I want to plot a time series of df1 as a line graph and i want to put markers on that trace at points where df2 “flag” column value = True at those points in time

How can i do this?