Hi
At least in this simple example in RStudio the width and height parameters are ignored:
plot_ly(economics, x = date, y = uempmed, mode = "markers", width = 200, height = 200)
The workaround that I've found is using the layout function which seems to work as expected:
plot_ly(economics, x = date, y = uempmed, mode = "markers") %>%
layout(width = 200, height = 200, autosize = FALSE)