diff --git a/deploy/synology_dsm.sh b/deploy/synology_dsm.sh
index cd8ef239..0a2bdf7a 100644
--- a/deploy/synology_dsm.sh
+++ b/deploy/synology_dsm.sh
@@ -9,26 +9,33 @@
 # Issues:  https://github.com/acmesh-official/acme.sh/issues/2727
 ################################################################################
 # Usage:
-# 1. Set required environment variables (two ways):
-# - Create temp admin user automatically
-#   `export SYNO_UseTempAdmin=1`
-# - Or provide your own admin user credential by:
+# 1. Set required environment variables:
+# - use automatically created temp admin user to authenticate
+#   1. disable "enfore 2FA-OTP for admins" via control panel
+#   2. `export SYNO_UseTempAdmin=1`
+# - or provide your own admin user credential to authenticate
 #   1. `export SYNO_Username="adminUser"`
 #   2. `export SYNO_Password="adminPassword"`
 # 2. Set optional environment variables (shown values are the defaults)
-# - `export SYNO_Scheme="http"`
-# - `export SYNO_Hostname="localhost"`
-# - `export SYNO_Port="5000"`
-# - `export SYNO_Create=1` - to allow creating the cert if it doesn't exist
-# - `export SYNO_Certificate=""` - to replace a specific cert by its description
-# - `export SYNO_DeviceName=""`  - required for 2FA-OTP
-# - `export SYNO_DeviceID=""`    - required for omitting 2FA-OTP (only pro
-#                                  users may set)
+# - common optional variables
+#   - `export SYNO_Scheme="http"`
+#   - `export SYNO_Hostname="localhost"`
+#   - `export SYNO_Port="5000"`
+#   - `export SYNO_Create=1` - to allow creating the cert if it doesn't exist
+#   - `export SYNO_Certificate=""` - to replace a specific cert by its
+#                                    description
+# - 2FA-OTP optional variables (with your own admin user)
+#   - `export SYNO_DeviceName=""`  - required for 2FA-OTP, script won't require
+#                                    interactive input the device name if set.
+#   - `export SYNO_OTPCode=""`     - required for 2FA-OTP, script won't require
+#                                    interactive input the code if set.
+#   - `export SYNO_DeviceID=""`    - required for omitting 2FA-OTP (might be
+#                                    deprecated, auth with OTP code instead)
 # 3. Run command:
 # acme.sh --deploy --deploy-hook synology_dsm -d example.com
 ################################################################################
 # Dependencies:
-# - jq & curl
+# - curl
 # - synouser & synogroup (When available and SYNO_UseTempAdmin is set)
 ################################################################################
 # Return value:
@@ -48,44 +55,48 @@ synology_dsm_deploy() {
   # Get username and password, but don't save until we authenticated successfully
   _getdeployconf SYNO_Username
   _getdeployconf SYNO_Password
-  _getdeployconf SYNO_DeviceName
   _getdeployconf SYNO_DeviceID
-  _getdeployconf SYNO_Create
+  _getdeployconf SYNO_DeviceName
 
   # ## START ## - DEPRECATED, for backward compatibility
   _getdeployconf SYNO_Device_ID
   _getdeployconf SYNO_Device_Name
-  [ -n "$SYNO_DeviceID" ] || SYNO_DeviceID="$SYNO_Device_ID"
-  [ -n "$SYNO_DeviceName" ] || SYNO_DeviceName="$SYNO_Device_Name"
+  [ -n "$SYNO_DeviceID" ] || SYNO_DeviceID="${SYNO_Device_ID:-}"
+  [ -n "$SYNO_DeviceName" ] || SYNO_DeviceName="${SYNO_Device_Name:-}"
   # ## END ## - DEPRECATED, for backward compatibility
-  [ -n "$SYNO_Create" ] || SYNO_Create=1
 
   # Prepare to use temp admin if SYNO_UseTempAdmin is set
   _getdeployconf SYNO_UseTempAdmin
   _debug2 SYNO_UseTempAdmin "$SYNO_UseTempAdmin"
 
+  # Back to use existing admin user if explicitly requested
+  if [ "$SYNO_UseTempAdmin" -eq 0 ]; then
+    _debug2 Back to use existing user rather than temp admin user.
+    SYNO_UseTempAdmin=""
+  fi
+  _savedeployconf SYNO_UseTempAdmin "$SYNO_UseTempAdmin"
+
   if [ -n "$SYNO_UseTempAdmin" ]; then
     if ! _exists synouser || ! _exists synogroup; then
       _err "Tools are missing for creating temp admin user, please set SYNO_Username and SYNO_Password instead."
       return 1
     fi
-    # Clean up
+
     [ -n "$SYNO_Username" ] || _savedeployconf SYNO_Username ""
     [ -n "$SYNO_Password" ] || _savedeployconf SYNO_Password ""
-    synouser --del "$SYNO_Username" >/dev/null 2>/dev/null
 
     _debug "Setting temp admin user credential..."
     SYNO_Username=sc-acmesh-tmp
     SYNO_Password=$(head /dev/urandom | tr -dc A-Za-z0-9 | head -c 16)
-    # Ignore 2FA-OTP settings which won't be needed.
+    # Set 2FA-OTP settings to empty consider they won't be needed.
     SYNO_DeviceID=
     SYNO_DeviceName=
-
-    _savedeployconf SYNO_UseTempAdmin "$SYNO_UseTempAdmin"
+    SYNO_OTPCode=
+    # Pre-delete temp admin user if already exists.
+    synouser --del "$SYNO_Username" >/dev/null 2>/dev/null
   else
     _debug2 SYNO_Username "$SYNO_Username"
     _secure_debug2 SYNO_Password "$SYNO_Password"
-    _debug2 SYNO_Create "$SYNO_Create"
     _debug2 SYNO_DeviceName "$SYNO_DeviceName"
     _secure_debug2 SYNO_DeviceID "$SYNO_DeviceID"
   fi
@@ -114,7 +125,7 @@ synology_dsm_deploy() {
 
   # Get the certificate description, but don't save it until we verify it's real
   _getdeployconf SYNO_Certificate
-  _debug SYNO_Certificate "$SYNO_Certificate"
+  _debug SYNO_Certificate "${SYNO_Certificate:-}"
 
   # shellcheck disable=SC1003 # We are not trying to escape a single quote
   if printf "%s" "$SYNO_Certificate" | grep '\\'; then
@@ -122,20 +133,6 @@ synology_dsm_deploy() {
     return 1
   fi
 
-  # Create temp admin user
-  if [ -n "$SYNO_UseTempAdmin" ]; then
-    _debug "Creating temp admin user in Synology DSM..."
-    synouser --add "$SYNO_Username" "$SYNO_Password" "" 0 "scruelt@hotmail.com" 0 >/dev/null
-    if [ -n "$(synogroup --help | grep '\-\-memberadd')" ]; then
-      synogroup --memberaddx administrators "$SYNO_Username" >/dev/null
-    else
-      # For supporting DSM 6.x which only has `--member` parameter.
-      cur_admins=$(synogroup --get administrators | awk -F '[][]' '/Group Members/,0{if(NF>1)printf "%s ", $2}')
-      _secure_debug3 admin_users "$cur_admins$SYNO_Username"
-      synogroup --memberx administrators $cur_admins $SYNO_Username >/dev/null
-    fi
-  fi
-
   _debug "Getting API version..."
   _base_url="$SYNO_Scheme://$SYNO_Hostname:$SYNO_Port"
   _debug _base_url "$_base_url"
@@ -151,7 +148,6 @@ synology_dsm_deploy() {
   encoded_username="$(printf "%s" "$SYNO_Username" | _url_encode)"
   encoded_password="$(printf "%s" "$SYNO_Password" | _url_encode)"
 
-  otp_code=""
   # ## START ## - DEPRECATED, for backward compatibility
   _getdeployconf SYNO_TOTP_SECRET
 
@@ -178,31 +174,85 @@ synology_dsm_deploy() {
     response=$(_post "method=login&account=$encoded_username&passwd=$encoded_password&api=SYNO.API.Auth&version=$api_version&enable_syno_token=yes&otp_code=$DEPRECATED_otp_code&device_name=certrenewal&device_id=$SYNO_DeviceID" "$_base_url/webapi/auth.cgi?enable_syno_token=yes")
     _debug3 response "$response"
   # ## END ## - DEPRECATED, for backward compatibility
-  # If SYNO_Device_ID & SYNO_DeviceName both empty, just log in normally
-  elif [ -z "${SYNO_DeviceID:-}" ] && [ -z "${SYNO_DeviceName:-}" ]; then
-    response=$(_get "$_base_url/webapi/entry.cgi?api=SYNO.API.Auth&version=$api_version&method=login&format=sid&account=$encoded_username&passwd=$encoded_password&enable_syno_token=yes")
-    _debug3 response "$response"
-  # Get device ID if still empty first, otherwise log in right away
-  # If SYNO_DeviceName is set, we treat that account enabled two-factor authorization, consider SYNO_DeviceID is not set, so it won't be able to login without requiring the OTP code.
-  elif [ -n "${SYNO_DeviceName:-}" ] && [ -z "${SYNO_DeviceID:-}" ]; then
+  # If SYNO_DeviceID or SYNO_OTPCode is set, we treat current account enabled 2FA-OTP.
+  # Notice that if SYNO_UseTempAdmin=1, both variables will be unset
+  else
+    if [ -n "$SYNO_UseTempAdmin" ]; then
+      _debug "Creating temp admin user in Synology DSM..."
+      synouser --add "$SYNO_Username" "$SYNO_Password" "" 0 "scruelt@hotmail.com" 0 >/dev/null
+      if synogroup --help | grep -q '\-\-memberadd'; then
+        synogroup --memberadd administrators "$SYNO_Username" >/dev/null
+      else
+        # For supporting DSM 6.x which only has `--member` parameter.
+        cur_admins=$(synogroup --get administrators | awk -F '[][]' '/Group Members/,0{if(NF>1)printf "%s ", $2}')
+        _secure_debug3 admin_users "$cur_admins$SYNO_Username"
+        # shellcheck disable=SC2086
+        synogroup --member administrators $cur_admins $SYNO_Username >/dev/null
+      fi
+    fi
+    if [ -n "$SYNO_DeviceID" ] || [ -n "$SYNO_OTPCode" ]; then
+      response='{"error":{"code":403}}'
+    # Assume the current account disabled 2FA-OTP, try to log in right away.
+    else
+      response=$(_get "$_base_url/webapi/entry.cgi?api=SYNO.API.Auth&version=$api_version&method=login&format=sid&account=$encoded_username&passwd=$encoded_password&enable_syno_token=yes")
+      _debug3 response "$response"
+    fi
+  fi
+
+  error_code=$(echo "$response" | grep '"error"' | grep -oP '(?<="code":)\d+')
+  # Account has 2FA-OTP enabled, since error 403 reported.
+  if [ "${error_code:-0}" -eq 403 ]; then
+    if [ -z "$SYNO_DeviceName" ]; then
+      printf "Enter device name or leave empty for default (CertRenewal): "
+      read -r SYNO_DeviceName
+      [ -n "$SYNO_DeviceName" ] || SYNO_DeviceName="CertRenewal"
+    fi
+
+    if [ -n "$SYNO_DeviceID" ]; then
+      # Omit OTP code with SYNO_DeviceID.
+      response=$(_get "$_base_url/webapi/$api_path?api=SYNO.API.Auth&version=$api_version&method=login&format=sid&account=$encoded_username&passwd=$encoded_password&enable_syno_token=yes&device_name=$SYNO_DeviceName&device_id=$SYNO_DeviceID")
+      _secure_debug3 response "$response"
+    else
+      # Require the OTP code if still unset.
+      if [ -z "$SYNO_OTPCode" ]; then
         printf "Enter OTP code for user '%s': " "$SYNO_Username"
-        read -r otp_code
-        response=$(_get "$_base_url/webapi/$api_path?api=SYNO.API.Auth&version=$api_version&method=login&format=sid&account=$encoded_username&passwd=$encoded_password&otp_code=$otp_code&enable_syno_token=yes&enable_device_token=yes&device_name=$SYNO_DeviceName")
+        read -r SYNO_OTPCode
+      fi
+
+      if [ -z "$SYNO_OTPCode" ]; then
+        response='{"error":{"code":404}}'
+      else
+        response=$(_get "$_base_url/webapi/$api_path?api=SYNO.API.Auth&version=$api_version&method=login&format=sid&account=$encoded_username&passwd=$encoded_password&enable_syno_token=yes&enable_device_token=yes&device_name=$SYNO_DeviceName&otp_code=$SYNO_OTPCode")
         _secure_debug3 response "$response"
 
         id_property='device_id'
         [ "${api_version}" -gt '6' ] || id_property='did'
         SYNO_DeviceID=$(echo "$response" | grep "$id_property" | sed -n 's/.*"'$id_property'" *: *"\([^"]*\).*/\1/p')
         _secure_debug2 SYNO_DeviceID "$SYNO_DeviceID"
-  # Otherwise, if SYNO_DeviceID is set, we can just use it to login.
-  else
-    if [ -z "${SYNO_DeviceName:-}" ]; then
-      printf "Enter device name or leave empty for default (CertRenewal): "
-      read -r SYNO_DeviceName
-      [ -n "${SYNO_DeviceName}" ] || SYNO_DeviceName="CertRenewal"
+      fi
     fi
-    response=$(_get "$_base_url/webapi/$api_path?api=SYNO.API.Auth&version=$api_version&method=login&format=sid&account=$encoded_username&passwd=$encoded_password&enable_syno_token=yes&device_name=$SYNO_DeviceName&device_id=$SYNO_DeviceID")
-    _secure_debug3 response "$response"
+    error_code=$(echo "$response" | grep '"error"' | grep -oP '(?<="code":)\d+')
+  fi
+
+  if [ -n "$error_code" ]; then
+    if [ "$error_code" -eq 403 ] && [ -n "$SYNO_DeviceID" ]; then
+      _savedeployconf SYNO_DeviceID ""
+      _err "Failed to authenticate with SYNO_DeviceID (may expired or invalid), please try again in a new terminal window."
+    elif [ "$error_code" -eq 404 ]; then
+      _err "Failed to authenticate with provided 2FA-OTP code, please try again in a new terminal window."
+    elif [ "$error_code" -eq 406 ]; then
+      if [ -n "$SYNO_UseTempAdmin" ]; then
+        _err "SYNO_UseTempAdmin=1 is not supported if enforce auth with 2FA-OTP is enabled."
+      else
+        _err "Enforce auth with 2FA-OTP enabled, please configure the user to enable 2FA-OTP to continue."
+      fi
+    elif [ "$error_code" -eq 400 ] || [ "$error_code" -eq 401 ] || [ "$error_code" -eq 408 ] || [ "$error_code" -eq 409 ] || [ "$error_code" -eq 410 ]; then
+      _err "Failed to authenticate with a non-existent or disabled account, or the account password is incorrect or has expired."
+    else
+      _err "Failed to authenticate with error: $error_code."
+    fi
+    _temp_admin_cleanup "$SYNO_UseTempAdmin" "$SYNO_Username"
+    return 1
   fi
 
   sid=$(echo "$response" | grep "sid" | sed -n 's/.*"sid" *: *"\([^"]*\).*/\1/p')
@@ -210,11 +260,9 @@ synology_dsm_deploy() {
   _debug "Session ID" "$sid"
   _debug SynoToken "$token"
   if [ -z "$sid" ] || [ -z "$token" ]; then
-    _err "Unable to authenticate to $_base_url - check your username & password."
-    _err "If two-factor authentication is enabled for the user:"
-    _err "- set SYNO_DeviceName then input *correct* OTP-code manually"
-    _err "- get & set SYNO_DeviceID via your browser cookies"
-    _remove_temp_admin "$SYNO_USE_TEMP_ADMIN" "$SYNO_Username"
+    # Still can't get necessary info even got no errors, may Synology have API updated?
+    _err "Unable to authenticate to $_base_url, you may report the full log to the community."
+    _temp_admin_cleanup "$SYNO_UseTempAdmin" "$SYNO_Username"
     return 1
   fi
 
@@ -223,12 +271,15 @@ synology_dsm_deploy() {
   _debug2 H1 "${_H1}"
 
   # Now that we know the username and password are good, save them if not in temp admin mode.
-  if [ -z "$SYNO_UseTempAdmin" ]; then
+  if [ -n "$SYNO_UseTempAdmin" ]; then
+    _savedeployconf SYNO_Username ""
+    _savedeployconf SYNO_Password ""
+  else
     _savedeployconf SYNO_Username "$SYNO_Username"
     _savedeployconf SYNO_Password "$SYNO_Password"
-    _savedeployconf SYNO_DeviceID "$SYNO_DeviceID"
-    _savedeployconf SYNO_DeviceName "$SYNO_DeviceName"
   fi
+  _savedeployconf SYNO_DeviceID "$SYNO_DeviceID"
+  _savedeployconf SYNO_DeviceName "$SYNO_DeviceName"
 
   _info "Getting certificates in Synology DSM..."
   response=$(_post "api=SYNO.Core.Certificate.CRT&method=list&version=1&_sid=$sid" "$_base_url/webapi/entry.cgi")
@@ -238,9 +289,24 @@ synology_dsm_deploy() {
   id=$(echo "$response" | sed -n "s/.*\"desc\":\"$escaped_certificate\",\"id\":\"\([^\"]*\).*/\1/p")
   _debug2 id "$id"
 
+  error_code=$(echo "$response" | grep '"error"' | grep -oP '(?<="code":)\d+')
+  if [ -n "$error_code" ]; then
+    if [ "$error_code" -eq 105 ]; then
+      _err "Current user is not administrator and does not have sufficient permission for deploying."
+    else
+      _err "Failed to fetch certificate info with error: $error_code, contact Synology for more info about it."
+    fi
+    _temp_admin_cleanup "$SYNO_UseTempAdmin" "$SYNO_Username"
+    return 1
+  fi
+
+  _getdeployconf SYNO_Create
+  _debug2 SYNO_Create "$SYNO_Create"
+  [ -n "$SYNO_Create" ] || SYNO_Create=1
+
   if [ -z "$id" ] && [ -z "$SYNO_Create" ]; then
     _err "Unable to find certificate: $SYNO_Certificate and $SYNO_Create is not set."
-    _remove_temp_admin "$SYNO_UseTempAdmin" "$SYNO_Username"
+    _temp_admin_cleanup "$SYNO_UseTempAdmin" "$SYNO_Username"
     return 1
   fi
 
@@ -275,11 +341,11 @@ synology_dsm_deploy() {
     else
       _info "Restarting HTTP services failed."
     fi
-    _remove_temp_admin "$SYNO_UseTempAdmin" "$SYNO_Username"
+    _temp_admin_cleanup "$SYNO_UseTempAdmin" "$SYNO_Username"
     _logout
     return 0
   else
-    _remove_temp_admin "$SYNO_UseTempAdmin" "$SYNO_Username"
+    _temp_admin_cleanup "$SYNO_UseTempAdmin" "$SYNO_Username"
     _err "Unable to update certificate, error code $response."
     _logout
     return 1
@@ -293,12 +359,12 @@ _logout() {
   _debug3 response "$response"
 }
 
-_remove_temp_admin() {
+_temp_admin_cleanup() {
   flag=$1
   username=$2
 
   if [ -n "${flag}" ]; then
-    _debug "Removing temp admin user in Synology DSM..."
+    _debug "Cleanuping temp admin info..."
     synouser --del "$username" >/dev/null
   fi
 }