I am trying to publish an app on shinyapps.io that works perfectly fine locally, but when I upload it online, I get the following error:

Error in func(fname, …) : app.R did not return a shiny.appobj object.

and this o the browser page:

An error has occurred
The application failed to start.

exit status 1

Here the code for the app:

library(shiny)
library("shinythemes")
library("randomForest")
library("data.table")
library("RCurl")
rf_model <- readRDS("rf_model1.rds")

###############################

ui <- fluidPage(
    theme = shinytheme("united"),
    titlePanel( "Maximal Ischemia Time Calculator"),
    sidebarPanel(
        sliderInput(inputId = "age",
                    label = "Age:",
                    min = 18,
                    max = 100,
                    value = 60,
                    step = 1), 
        
        selectInput(inputId = "cci", 
                    label = "CCI:", 
                    choices = list("0" = "0", "1" = "1", "2" = "2", "3+" = ">2"), 
                    selected = "0"),
        
        selectInput(inputId = "asa", 
                    label = "ASA score:", 
                    choices = list("1" = "1", "2" = "2", "3" = "3", "4" = "4"), 
                    selected = "1"),
        
        selectInput(inputId = "hypertension", 
                    label = "Hypertension:", 
                    choices = list("Yes" = "1", "No" = "0"), 
                    selected = "No"),
        
        sliderInput(inputId = "hb.pre",
                    label = "Preoperative Hb:",
                    min = 3.0,
                    max = 20.0,
                    value = 13.0,
                    step = 0.1),
        
        sliderInput(inputId = "gfr.pre",
                    label = "Preoperative eGFR:",
                    min = 10.0,
                    max = 150.0,
                    value = 60.0,
                    step = 0.1),
        
        sliderInput(inputId = "c.size",
                    label = "Tumour dimensions (cm):",
                    min = 0.1,
                    max = 20.0,
                    value = 2.0,
                    step = 0.1),
        
        selectInput(inputId = "renal.class", 
                    label = "RENAL Score:", 
                    choices = list("Low Risk" = "1", "Intermediate Risk" = "2", "High Risk" = "3"), 
                    selected = "Low Risk"),
        
        actionButton("submitbutton", "Submit", class = "btn btn-primary")),
    
    mainPanel
    (
        tags$label(h3('Results')), # Status/Output Text Box
        verbatimTextOutput('contents'),
        verbatimTextOutput('results')
    ))

server <- function(input, output, session) {
    datasetInput <- reactive({  
        df <- data.frame(
            Name = c("age",
                     "cci",
                     "asa",
                     "hypertension",
                     "hb.pre",
                     "gfr.pre",
                     "c.size",
                     "renal.class"),
            Value = as.character(c(input$age,
                                   input$cci,
                                   input$asa,
                                   input$hypertension,
                                   input$hb.pre,
                                   input$gfr.pre,
                                   input$c.size,
                                   input$renal.class)),
            stringsAsFactors = FALSE)
        
        ischemia.time <- "ischemia.time"
        df <- rbind(df, ischemia.time)
        input <- transpose(df)
        write.table(input,"input.csv", sep=",", quote = FALSE, row.names = FALSE, col.names = FALSE)
        
        test <- read.csv(paste("input", ".csv", sep=""), header = TRUE)
        
        test$age <- as.numeric(test$age)
        test$hb.pre <- as.numeric(test$hb.pre)
        test$gfr.pre <- as.numeric(test$gfr.pre)
        test$c.size <- as.numeric(test$c.size)
        test$cci <- factor(test$cci, levels = c("0", "1", "2", ">2"))
        test$asa <- factor(test$asa, levels = c("1", "2", "3", "4"))
        test$hypertension <- factor(test$hypertension, levels = c("1", "0"))
        test$renal.class <- factor(test$renal.class, levels = c("1", "2", "3"))
        
        
        find_max_ischemia_time <- function(data, rf_model, p.critico) 
        {
            t_min <- 1
            t_max <- 60
            t_final <- t_min
            while (t_final < t_max) 
            {
                data$ischemia.time <- as.numeric(t_final)
                p_danno <- (predict(rf_model, data , type = "prob")[,2])
                if (p_danno <= p.critico) 
                {
                    t_final <- t_final + 1  # Aumenta il tempo minimo
                } 
                else 
                {
                    t_result <- t_final
                    return(t_result)
                }
            }
            return(t_result)
        }
        
        Output <- find_max_ischemia_time(test, rf_model, p.critico = 0.10)
        print(paste("The recommended maximum ischemia time is:", Output, "minutes"))
    })
    
    # Status/Output Text Box
    
    
    output$contents <- renderPrint({
        if (input$submitbutton>0) { 
            isolate("Calculation complete.") 
        } else {
            return("Server is ready for calculation.")
        }
    })
    
    # Prediction results table
    output$results <- renderPrint({
        if (input$submitbutton>0) { 
            isolate(datasetInput())
        }})
}

shinyApp(ui = ui, server = server)

I tried debugging my code but i don’t see anything that seems wrong to me