Rshiny won't accept any inputID except "file"

Question

no idea what the problem is here. Any time I give an inputID to fileInput other than "file", I'll get an error saying "Error: '[inputID here]' not found."

ui <- fluidPage(
    titlePanel("BF591 Final"),
    sidebarPanel(
        fileInput("file1", "Upload metadata in CSV or TSV format.", accept = c(".csv", ".tsv"))
    ),
    mainPanel(
        tableOutput("sample_info_tb")
    )
)
server <- function(input, output) {
    load_meta <- reactive({
        if(is.null(file1)){return()}
        metadata_df <- read.csv(input$file1$datapath, row.names=1)
        return(metadata_df)
    })
    
    options(shiny.maxRequestSize=30*1024^2)

    output$sample_info_tb <- renderTable({
        req(input$file1)
        load_meta()
    })
}
shinyApp(ui = ui, server = server)