Stamen map not rendered in shiny -> receiving blank image

I try to build some simple stamenmaps with ggmap in R-Shiny. I can't seem to get the map rendered. I only receive a blank image. The the simple example attached below:

```r
library(ggmap)
library(shiny)

server <- function(input, output) {

map_ren <- renderPlot(get_stamenmap(
bbox = c(
left = 10,
bottom = 30,
right = 42,
top = 34),
maptype = "terrain",
zoom = 3,
force = TRUE
), width = 1000, height = 1000)

output$map <- map_ren
}

ui <- fluidPage(
plotOutput('map', width = 1000, height = 1000)
)

shinyApp(ui, server)

}, si = TRUE)
```

Start by running the minimal ggmap and Shiny example from the issue, focusing on get_stamenmap and renderPlot. Confirm the failure and isolate whether the blank output comes from map retrieval or Shiny rendering; done means the Stamen terrain map appears in the plot output.

Written by the indexing model from the issue text.