The following is a simple application where that use a InfoBox
.
I tried to use the same parameters as your example, except I used value = 20.
library(shiny)
library(shinydashboard)
ui <- dashboardPage(
dashboardHeader(title = "Info boxes"),
dashboardSidebar(),
dashboardBody(
#Show infobox in ui
infoBoxOutput("id")
)
)
server <- function(input, output) {
output$id <- renderInfoBox({
infoBox(
#We only have 3 parameters to show information
title = "title",
value = 20,
subtitle = "description",
icon = icon("question-circle")
)
})
}
shinyApp(ui, server)

As already mentioned we only have 3 parameters to write or display information: title, value and subtitle.
You were trying to put an icon in the subtitle parameter, and this should go in the icon parameter.
Then you can use the subtitle parameter to write several lines if you wish.
subtitle = tags$a(icon("question-circle"),"This ia a descrpcion"))

If you are looking to make a more complex design you should check the Box function.