Changing Chloropleth Maps based on input in R Shiny

I am using ggplot to plot chloropleth maps of the UK based on investment from US to UK. This can be catagorised by either 'Projects', 'Avg Capex' or 'Jobs'. I want to fill the map with colour depending on which of the 3 previous variables is selected.

At the moment my app is only displaying a uniform colour regardless of which option I press. The code works when not in shiny but I can't get it to work in shiny!

My code for the UI and server

ui <- fluidPage(
  titlePanel("North America Investment 2019"),
  selectInput(inputId = "group_select", label = "Investment Measure", 
              choices = colnames(together)[c(8,10,11)], selected = colnames(together)[8]),
  plotOutput('plot')
)

server <- function(input, output) {

  g <- ggplot(together, aes(x = long, y = lat, group = group), col = "black") +
    geom_polygon(aes(fill = input$group_select))
  output$plot <-  renderPlot(g)

}

shinyApp(ui = ui, server = server)

where my colnames(togther) are

 [1] "long"         "lat"          "order"        "hole"         "piece"       
 [6] "group"        "id"           "Projects"     "Capex"        "Avg capex"   
[11] "Jobs created" "Avg jobs"     "Companies" 

This is my first time using RShiny