How to use a non-default colorscale in R plotly chloropleth maps?

I'm creating a chloropleth map in R using plotly, and the only trouble I'm having is setting a different colorscale. I would like to use the magma colorscale from the viridis package, but I can't seem to figure out the correct way to do it. I've tried googling and searching, but no answers are quite working. Anyone have any advice?

The error I'm getting is: "unique() only applies to vectors." I've tried setting "discrete = TRUE" but that does not work.

Let me know if you need more information.

create_cw_map <- function(data, color_var) {
  if (is.null(data))
    return(NULL)

  g <- list(scope = "usa",
           projection = list(type = "albers usa"),
           showlakes = FALSE)

  cw_map <- plot_geo(data,
                     locationmode = "USA-states") %>%
            add_trace(z = ~ get(color_var),
                      locations = ~ state,
                      color = ~ get(color_var),
                      colorscale =  scale_fill_viridis(option = "magma")) %>%
            colorbar(title = color_var) %>%
            layout(geo = g)

            print(cw_map)
}