I've found this question but answer is not up to date to produce the correct result.
Second Y-Axis in a R plotly graph
How can I plot a dual y axis plot?
df <- data.frame(MediaDate = as.Date(c("2016-04-01","2016-05-01","2016-06-01"), format = "%Y-%m-%d"),
Spend = c(39654, 34446, 27402),
Visits = c(19970, 14450, 12419))
plot_ly(df, x = ~MediaDate, y = ~Spend, type = "bar", name = "Spend") %>%
add_trace(x = ~MediaDate, y = ~Visits, mode = "lines", yaxis = "y2", name = "Visits") %>%
layout(yaxis2 = list(overlaying = "y", side = "right"))
Produces:
What I need (but instead of a bar and a line, 2 lines):


