Targeting/Adding traces in subplot

Hi - I'm trying to add/change traces in a graph with subplots. Below the example code.

It looks like each subplot becomes one trace (based on playing with the restyle section), but it is unclear to me how to add/remove traces. I changed the addTraces number at the end to 0-3 but it always adds it to the first subplot.

Any help would be appreciated.

data <- tibble(runmonth=c(1,1,1,1,4,4,4,4),variable=c('a','a','b','b','a','a','b','b'),x=c(1:8),y=c(8:1),keyname=paste0('k',c(1:8)))

p <- data %>% group_by(runmonth,variable) %>%
  do(
    p = highlight_key(., ~keyname,group='scattergroup') %>%
      plot_ly(showlegend = FALSE) %>%
      add_markers(
        x = ~x, y = ~y
      )
  ) %>%
  subplot(
    nrows = 2, margin = 0.01,
    shareY = TRUE, shareX = TRUE, titleY = FALSE
  ) %>% toWebGL() %>%
  highlight(
    on = "plotly_selected",
    off = c('plotly_relayout')
  )


ui <- function(id) {
  div(
    actionButton('go','go'),
    plotlyOutput("scattergr")
  )
}

server <- function(input,output,session) {
  
  output$scattergr <- renderPlotly({p})
  
  observeEvent(input$go,{
    plotlyProxy("scattergr", session) %>%
      plotlyProxyInvoke(
        "restyle",
        list(
          'marker.symbol' = list(c(rep('triangle-up',1),'circle'))
        ),
        list(0,1,2,3)
      ) %>%
      plotlyProxyInvoke(
        "addTraces",
        list(
          x = c(50,60),
          y = c(50,60),
          mode = "scatter"
        ),1
      ) %>%
      plotlyProxyInvoke(
        "moveTraces",
        -1,0
      )
  })
  

}

runApp(shinyApp(ui, server))

Use the supplied Shiny reproduction as the starting point, focusing on the plotlyProxyInvoke calls for restyle, addTraces, and moveTraces in the subplot example. Determine the expected trace indexing behavior for subplots and whether the result should be a code correction or clearer documentation; done means the requested traces can be targeted predictably.