Try to config the 404.html file

Remove error page 50X

conf/nginx.conf

@@ -25,11 +25,6 @@ location __PATH__/ {
     location = __PATH__/error/404.html {
         internal;
     }
-    error_page 500 502 503 /50x.html;
-    location = __PATH__/error/50x.html {
-        internal;
-    }
-
 
     # Deny access to hidden files and directories
     location ~ ^__PATH__/(.+/|)\.(?!well-known\/) {

config_panel.toml

@@ -18,6 +18,14 @@ name = "My Webapp configuration"
         visible = "with_sftp"
         help = "If a password already exist, leave blank and it will not be replaced."
 
+    [main.error]
+    name = "Html Custom error"
+
+        [main.error.setting]
+        ask = "HTML Path"
+        type = "string"
+        default = "/404.html"
+
     [main.php_fpm_config]
     name = "PHP-FPM configuration"