R: Use of shinyAlert() in case of typo

I have a reprex in the form of a data.table with two variables. One of them is a date column with drop-down calendars. I want a shinyAlert() to pop up when I by mistake type something in a cell of the date column instead of choosing from the calendar. I have inserted shinyAlert() in a relevant place of the snippet but it is popping up automatically as well as when I type a text by mistake or choose from the calendar properly.

Can someone show me what is wrong with my code?

 library(shiny)
 library(rhandsontable)
 library(data.table)
 library(shinyalert)

 DF <- data.table(Date = as.character(Sys.Date()), col1 = as.numeric(c(1, 2, 3)))

 ui <- fluidPage(
   useShinyalert(),
   rHandsontableOutput("table")
 )

 server <- function(input, output, session) {

    data <- reactiveValues()

   observe({
     data$df <- as.data.table(DF)
   })

 observeEvent(input$table, {
   if (!is.null(input$table)) {
     df <- hot_to_r(input$table)
     # Check if the Date column is in a valid format
     valid_dates <- !is.na(as.Date(df$Date, format = "%Y-%m-%d"))
     if (any(!valid_dates)) {
       shinyalert("Invalid Date", "Please enter a valid date format (YYYY-MM-DD).", type = "error")
     }
   }
 })

   output$table <- renderRHandsontable({
     rhandsontable(data$df) |>
       hot_col(1, dateFormat = "YYYY-MM-DD", type = "date")
   })
 }
 shinyApp(ui, server)

This works fine for me. Please note that I am using anydate() function from anytime package.

observeEvent(input$table, {
    if (!is.null(input$table)) {
      df <- hot_to_r(input$table)
      print(any(is.na(as.character(anydate(df$Date)))))
      if (any(is.na(as.character(anydate(df$Date))))) {
        shinyalert("Invalid Date", "Please enter a valid date format.", type = "error")
      }
    }
  })