R Shiny app working locally but not on shiny server - r

Question

My shiny app reads in an external csv file, updates it using user inputs in the app and updates the external csv file with these. This works locally however with my app on the shiny server it does not update, any idea why this is? Thanks.
I've added some simplistic code below but not really sure if it makes sense, the function num is meant to take the inputs, search for them in data frame and update and then output updated data frame and another data frame called "numbers" with timestamp.
The stuff with the modals at the bottom is that the num() function only happens when button is pressed, this creates modals with shows user what they have inputted and if they press 'proceed' the csv is updated if not they can go back and change details.
ui <- fluidPage(
useShinyjs(),
selectInput("1", "Pick a number", "1-2","2-3"),
selectInput("2", "Pick another number", "4-5", "5-6"),
actionButton("go", "Go")
)
server <- function(input, output, session){
df <- read.csv(df.csv, header = TRUE, sep = ",")
num <- function(df, num1, num2){
date.stamp <- format(Sys.time(), "%Y-%m-%d-%H-%M-%S")
save.file <- paste0("numbers", date.stamp, ".csv")
write.csv(df, file = save.file, row.names = FALSE)
write.csv(df, file = "df.csv", row.names = FALSE)
return(df)
}
observe({
shinyjs::toggleState("go", condition = isTruthy(input$1)
&& isTruthy(input$2))
})
react <- reactiveValues()
observeEvent(input$go, {
react$colm1 <- input$1
react$colm2 <- input$2
react$df1 <- data.frame("Numbers" = c("Num1", "Num2"),
"Values" = c(react$colm1, react$colm2))
react$review <- datatable(rownames = FALSE,
selection = "none",
options = list(dom = "t",
pageLength = nrow(rv$df.check),
autoWidth = FALSE,
columnDefs = list(list(width =
"20%",
targets = c(1)),
list(className = "dt-center",
targets = c(1)))),
react$df.check)
showModal(
modalDialog(
footer = tagList(modalButton("Change numbers"),
actionButton("click", label = "Proceed")
),
strong(em("Inputs Entered")),
p("Please double check numbers"),
DT::renderDataTable({
react$review
})
))
observeEvent(input$click, {
num(df, input$1, input$2)
shinyjs::reset("1");shinyjs::reset("s2")
removeModal()
})
})}
shinyApp(ui = ui, server = server) #calls shiny app