ggplot within shiny renderPlot(), when passing input$myinput, input not found

In my Shiny app, I have a ggplot which is supposed to update based on user inputs. However, for one of these inputs I am receiving an error of the form "Error: object [input$myinput] not found" e.g. "Error: object 'Channel' not found" or "Error: object 'UserType' not found" where Channel and UserType are selected input options.

In ui, the input looks like this:

selectInput(inputId = "breakdown", 
    label =  "Breakdown", 
    choices = c("Channel", "UserType", "Device"),
    selected = c("Channel"), 
    multiple = F)

This works in that I see the input on the UI when running the app.

However, I try to render this ggplot:

output$timeline <- renderPlot({      
  ggplot(ecom_channel(), aes_string(x = "Date", y = input$kpi_overlay, fill = input$breakdown, group = input$breakdown)) +
    geom_area(alpha = 0.3) +
    stat_summary(aes(group = 2), fun.y = sum, geom = 'line', size = 2, alpha = 0.5)
})

Since the select input being referenced in input$breakdown defaults to 'Channel', when I run the app I see:

Error: Object 'Channel' not found

I added a print line to see what the dataframe looks like in the console:

output$timeline <- renderPlot({      

print(ecom_channel() %>% glimpse())

  ggplot(ecom_channel(), aes_string(x = "Date", y = input$kpi_overlay, fill = input$breakdown, group = input$breakdown)) +
    geom_area(alpha = 0.3) +
    stat_summary(aes(group = 2), fun.y = sum, geom = 'line', size = 2, alpha = 0.5)
})

Adding that glimpse() line, in my console when I try to run I see:

Listening on http://127.0.0.1:7472
Observations: 0
Variables: 6
Groups: Date [0]
$ Date              <date> 
$ `input$breakdown` <chr> 
$ DailyUsers        <dbl> 
$ Sessions          <dbl> 
$ Transactions      <dbl> 
$ Revenue           <dbl> 
# A tibble: 0 x 6
# Groups:   Date [0]
# … with 6 variables: Date <date>, `input$breakdown` <chr>, DailyUsers <dbl>, Sessions <dbl>, Transactions <dbl>, Revenue <dbl>
Warning: Error in FUN: object 'Channel' not found
  183: FUN
  182: lapply
  181: scales_add_defaults
  180: f
  179: l$compute_aesthetics
  178: f
  177: by_layer
  176: ggplot_build.ggplot
  174: print.ggplot
  166: func
  164: f
  163: Reduce
  154: do
  153: hybrid_chain
  125: drawPlot
  111: <reactive:plotObj>
   95: drawReactive
   82: origRenderFunc
   81: output$timeline
    1: shiny::runApp
Observations: 28
Variables: 6
Groups: Date [28]
$ Date              <date> 2019-12-05, 2019-12-06, 2019-12-07, 2019-12-08, 2019-12-09, 2019-12-10, 2019-12-11, 2019-12-12, 2019-12-13, 2019-12-14, 2019-12-15, 2019-12-16, 2019-12-17, 2019-12…
$ `input$breakdown` <chr> "Channel", "Channel", "Channel", "Channel", "Channel", "Channel", "Channel", "Channel", "Channel", "Channel", "Channel", "Channel", "Channel", "Channel", "Channel",…
$ DailyUsers        <dbl> 292704, 265438, 236503, 270920, 326259, 306807, 289131, 277410, 254716, 223153, 249992, 301426, 278872, 259034, 244677, 236412, 197231, 195590, 212663, 165714, 1427…
$ Sessions          <dbl> 333310, 302817, 271243, 312109, 374986, 352259, 331171, 316371, 291096, 255558, 286597, 378436, 318979, 294888, 277761, 266630, 224764, 223705, 243362, 189518, 1611…
$ Transactions      <dbl> 2812, 2459, 2095, 3087, 3627, 3193, 2959, 2875, 2454, 2095, 2716, 3686, 2635, 2226, 2012, 1728, 1438, 1401, 1592, 973, 686, 970, 1036, 973, 1015, 1289, 1015, 1169
$ Revenue           <dbl> 128285.16, 113648.42, 92506.31, 138441.65, 145487.84, 140525.09, 127945.22, 117019.76, 112708.56, 91183.73, 114613.39, 148732.87, 114393.25, 90331.70, 84585.31, 700…
# A tibble: 28 x 6
# Groups:   Date [28]
   Date       `input$breakdown` DailyUsers Sessions Transactions Revenue
   <date>     <chr>                  <dbl>    <dbl>        <dbl>   <dbl>
 1 2019-12-05 Channel               292704   333310         2812 128285.
 2 2019-12-06 Channel               265438   302817         2459 113648.
 3 2019-12-07 Channel               236503   271243         2095  92506.
 4 2019-12-08 Channel               270920   312109         3087 138442.
 5 2019-12-09 Channel               326259   374986         3627 145488.
 6 2019-12-10 Channel               306807   352259         3193 140525.
 7 2019-12-11 Channel               289131   331171         2959 127945.
 8 2019-12-12 Channel               277410   316371         2875 117020.
 9 2019-12-13 Channel               254716   291096         2454 112709.
10 2019-12-14 Channel               223153   255558         2095  91184.
# … with 18 more rows

The idea is that I would like my ggplot to break out the selected metric by one of the 3 possible input dimensions of Channel, UserType or Device.

How can I do this?