raster works on local shiny app but not on shinyapps.io

I'm attempting to place an image into a leaflet map so that I can make markings on top of it. This all works well locally, but fails when running on shinyapps.io with the message:

Error: An error has occurred. Check your logs or contact the app author for clarification.

However, the logs are completely blank, without a single message. Here's a reprex of the issue:

title: "Raster Reprex"
runtime: shiny

# library(tidyverse)
# library(leaflet)

# this is the line that causes the error:
raster_img <- raster(
  band = 1,
  crs = "+proj=utm +zone=31 +datum=WGS84 +units=m +no_defs +ellps=WGS84 +towgs84=0,0,0",

# renderLeaflet({
#   leaflet() %>% 
#     addRasterImage(raster_img, colors = c("#000000", "#FFFFFF"))
# })

The uncommented code is all that is required to cause the issue on shinyapps.io. The rest is to provide context for my goal. If there's a better way to accomplish the same goal that goes around this issue, that would be fine as well. What is the issue with running raster on shinyapps.io?