I am working on a shiny app that can generate a determined number of UI outputs in form of inputs based on a value defined by the user. Thanks to the help of @YBS I was able to get the app working. But now I face a new issue. Although I could define min and max value for the inputs generated, I would like to add a warning in the inputs when a value is greater than 100, I found shinyfeedback package can do this but I do not where to put properly the code or what to do in the case of dinamyc inputs like the ones generated here. This is the working app:

library(shiny)
library(shinydashboard)
library(DT)
library(shinyFeedback)
#Function

compute <- function(firstitem,seconditem)
{
  Sum <- firstitem+seconditem
  Difference <- firstitem+seconditem
  Product <- firstitem*seconditem
  Ratio <- firstitem/seconditem
  Res <- data.frame(C1=Sum,C2=Difference,C3=Product,C4=Ratio)
  return(Res)
}

#App

ui = shinyUI(fluidPage(
  
  titlePanel("Compare"),
  
  sidebarLayout(
    sidebarPanel(
      numericInput("numitems", label = "Number of items to compare?",
                   min = 1, max = 100, value = 1),
      uiOutput("period_cutpoints"),
      uiOutput("period_cutpoints2"),
      actionButton("submit", "Submit")
    ),
    mainPanel(
      uiOutput("t1")
    )
  )
))

server = shinyServer(function(input, output, session) {
  
  output$period_cutpoints<-renderUI({
    req(input$numitems)
    lapply(1:(input$numitems), function(i) {
      numericInput(inputId=paste0("firstitem",i), 
                   label=paste0("Enter the value of first item ", i, ":"),value = i)
    })
    
  })
  
  output$period_cutpoints2<-renderUI({
    req(input$numitems)
    lapply(1:(input$numitems), function(i) {
      numericInput(inputId=paste0("seconditem",i), 
                   label=paste0("Enter the value of second item ", i, ":"),value = i+i)
    })
  })
  
  seldates <- reactiveValues(x=NULL)
  observeEvent(input$submit, {
    seldates$x <- list()
    lapply(1:(input$numitems), function(i) { 
      seldates$x[[i]] <- compute(firstitem = input[[paste0("firstitem", i)]],seconditem = input[[paste0("seconditem", i)]])
    })
  })
  
  observeEvent(input$submit, {
    
    lapply(1:(input$numitems), function(i) { 
      output[[paste0("table",i)]] <- renderDT(seldates$x[[i]])
    })
    
    output$t1 <- renderUI({
      tagList(
        lapply(1:(input$numitems), function(i) { 
          DTOutput(paste0("table",i))
        })
      )
    })
    
  })
  
})

shinyApp(ui = ui , server = server)

I tried to add some code inside the dynamic inputs in this way:

#Code demo
  output$period_cutpoints<-renderUI({
    req(input$numitems)
    lapply(1:(input$numitems), function(i) {
      numericInput(inputId=paste0("firstitem",i), 
                   label=paste0("Enter the value of first item ", i, ":"),value = i)
    })
    
    lapply(1:(input$numitems), function(i) {
      observeEvent(input[[paste0('firstitem',i)]], {
        shinyFeedback::feedbackWarning(
          inputId = paste0('firstitem',i),
          show = input[[paste0('firstitem',i)]] > 100,
          text = "Number less than 100 required.",
          color="red"
        )
      })
    })
    
  })

Unfortunately, this action broke down the app:

And the first input was not generated as you can see.

How can I solve this issue so that I can have warnings when the value is greater than 100? Moreover, this leads to an additional fact, in the action button if working with multiple inputs generated dynamically, how could I do something like this:

#How to extend the if condition so that it can consider the number of inputs defined by the user
observeEvent(input$submit,
             {
               if(input$firstitem1 < 0 && input$seconditem1 < 0 && input$firstitem2<0 && input$seconditem1<0)
               {
                 showModal(modalDialog(title ="Warning!!!", "Check fields!!!",easyClose = T))
               }
               else
               {
                 showModal(modalDialog(title ="Congratulations!!!", "Computing Done!!!",easyClose = T))
                 
               }
             })

How could I change the if so that it considers all the inputs that can be generated.

Many thanks!