Shiny App not working on Shiny Server with no log file present

Question

I have an application that works on a local R server (port 8787). When I move it to Shiny Server (port 3838), I receive the message

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

And there is no log file present in /var/log/shiny-server.log

This is my configuration file:

# Instruct Shiny Server to run applications as local user
run_as : HOME_USER:;

# Define a server that listens on port 3838
server {
  listen 3838;

#preserve_logs true;
  # Define a location at the base URL
 location / {

# Host the directory of Shiny Apps stored in this directory
site_dir /srv/shiny-server;

# Log all Shiny output to files in this directory
log_dir /var/log/shiny-server;
preserve_logs true;
# When a user visits the base URL rather than a particular application,
# an index of the applications available in this directory will be shown.
directory_index on;
 }
} 

Could someone check my configuration file? Thank you

Answer 1

Apparently sanitize error messages is true by default for my configuration. Add
options(shiny.sanitize.errors = FALSE) to your app.

In the configuration file, place

sanitize_errors false;
preserve_logs true;

within server to resolve permanently.

Answer 2

Shiny also dumps errors and messages on the Console. You can access it by pressing Ctrl + Shift + J in your chrome or Opera browser.