How to select a specific folder and then evaluate multiple files in Shiny (spectroscopic files involving ChemoSpec packages)

[eugenio.alladio]

I'd like to use a convert my code into a simple Shiny app, aimed to upload some spectroscopic data (in .jdx format) from a specific folder and, then, evaluatin them using ChemoSpec of readJDX packages.
I prepared the following R code that correctly works in the R environment:

library(ChemoSpec)
a<-getwd()
spec <- files2SpectraObject(
  gr.crit = "samples", freq.unit = "ppm", int.unit = "intensity",
  descrip = "test import", fileExt = "\\.JDX", path = a
)
dat <- spec$data

However, when I try to convert it in the R Shiny environment, I keep on obtaining errors. I prepared the following code:

library(shiny)
library(shinyFiles)
library(ChemoSpec)
library(DT)

ui <- fluidPage(
    
    shinyDirButton('folder', 'Folder select', 'Please select a folder', FALSE),
    textOutput("dir"),
    dataTableOutput("rendered_file")
)

server <- function(input,output,session){
    
    observe({  
        if(!is.null(input$folder)){
            shinyDirChoose(input, 'folder', roots=getVolumes())
            output$dir <- renderText(as.character(input$folder))
            }
    })
    
    dir <- reactive({
        input$folder
    })

    goButton <- eventReactive(input$folder,{
        spec <- files2SpectraObject(
            gr.crit = "campione", freq.unit = "ppm", int.unit = "intensity",
            descrip = "test import", fileExt = "\\.JDX", path = input$folder)
        spec$data
    })

    output$rendered_file <- DT::renderDataTable({
     req(input$folder)
     goButton()
     })
}
shinyApp(ui = ui, server = server)

but I keep on obtaining the following error:

Error in : operator is invalid for atomic vectors

I'd be extremely grateful if anybody could help me with this matter!