library(shiny)
library(shinydashboard)
library(leaflet)
library(dplyr)
library(htmltools)
library(gsheet)

shinyApp(

  ui <- fluidPage(
   
    leafletOutput("myMap", width="100%", height="100%"),
    titlePanel("eBird Visualizer"),
    fileInput("MyEBirdData_in", "MyEBirdData", multiple = FALSE, buttonLabel = "Upload a .csv", 
              placeholder = "No File Selected...", width = "255px")
  ),
  
  server = function(input, output) {
    
    myData = reactive(input$MyEBirdData_in) # I think this is where the problem is.

    df0 = data.frame(myData$Submission.ID, myData$Latitude, myData$Longitude)
    df = unique(df0)
    names(df)[2] = 'latitude'
    names(df)[3] = 'longitude'

    circleIcon = makeIcon(
      iconUrl = "http://www.clker.com/cliparts/Q/l/D/8/k/m/red-circle-icon-md.png",
      iconWidth = 7, iconHeight = 7)

    eBirdMap = leaflet(data = df) %>% addProviderTiles(providers$CartoDB.Positron) %>%
      addMarkers(icon = circleIcon)

    output$myMap = renderLeaflet(eBirdMap)
  }
)

Here's the error:

Warning: Error in $: object of type 'closure' is not subsettable
Stack trace (innermost first):
    38: data.frame
    37: server [/Users/Guest/Desktop/My_eBirdVisualizer/My_eBirdVisualizer.R#25]
     1: runApp
Error in myData$Submission.ID : 
  object of type 'closure' is not subsettable