diff --git a/config b/config
index d96751ee..8158bf80 100644
--- a/config
+++ b/config
@@ -33,4 +33,5 @@
 # classify_as_big_delete = "1000"
 # user_agent = ""
 # remove_source_files = "false"
-# skip_dir_strict_match = "false"
\ No newline at end of file
+# skip_dir_strict_match = "false"
+# application_id = ""
diff --git a/docs/USAGE.md b/docs/USAGE.md
index fbe76673..5cc41254 100644
--- a/docs/USAGE.md
+++ b/docs/USAGE.md
@@ -286,6 +286,7 @@ The default configuration file is listed below:
 # user_agent = ""
 # remove_source_files = "false"
 # skip_dir_strict_match = "false"
+# application_id = ""
 ```
 
 
diff --git a/src/config.d b/src/config.d
index fdbfbaef..7ab730f7 100644
--- a/src/config.d
+++ b/src/config.d
@@ -71,6 +71,9 @@ final class Config
 		boolValues["remove_source_files"] = false;
 		// Strict matching for skip_dir
 		boolValues["skip_dir_strict_match"] = false;
+		// Allow for a custom Client ID / Application ID to be used to replace the inbuilt default
+		// This is a config file option ONLY
+		stringValues["application_id"]       = "";
 
 		// Determine the users home directory. 
 		// Need to avoid using ~ here as expandTilde() below does not interpret correctly when running under init.d or systemd scripts
diff --git a/src/onedrive.d b/src/onedrive.d
index ad842a58..86a26a42 100644
--- a/src/onedrive.d
+++ b/src/onedrive.d
@@ -15,15 +15,6 @@ private bool simulateNoRefreshTokenFile = false;
 private ulong retryAfterValue = 0;
 
 private immutable {
-	// Client Identifier
-	// Client ID (skilion)
-	string clientId = "22c49a0d-d21c-4792-aed1-8f163c982546";
-	
-	// Default User Agent configuration
-	string isvTag = "ISV";
-	string companyName = "abraunegg";
-	string appTitle = "OneDrive_Client_for_Linux";
-	
 	// Personal & Business Queries
 	string authUrl = "https://login.microsoftonline.com/common/oauth2/v2.0/authorize";
 	string redirectUrl = "https://login.microsoftonline.com/common/oauth2/nativeclient";
@@ -36,10 +27,22 @@ private immutable {
 }
 
 private {
-    string driveUrl = "https://graph.microsoft.com/v1.0/me/drive";
-    string itemByIdUrl = "https://graph.microsoft.com/v1.0/me/drive/items/";
-    string itemByPathUrl = "https://graph.microsoft.com/v1.0/me/drive/root:/";
-    string driveId = "";
+	// Client ID / Application ID (abraunegg)
+	string clientId = "d50ca740-c83f-4d1b-b616-12c519384f0c";
+
+	// Default User Agent configuration
+	string isvTag = "ISV";
+	string companyName = "abraunegg";
+	// Application name as per Microsoft Azure application registration
+	string appTitle = "OneDrive Client for Linux";
+
+	// Default Drive ID
+	string driveId = "";
+
+	// Common URL's
+	string driveUrl = "https://graph.microsoft.com/v1.0/me/drive";
+	string itemByIdUrl = "https://graph.microsoft.com/v1.0/me/drive/items/";
+	string itemByPathUrl = "https://graph.microsoft.com/v1.0/me/drive/root:/";
 }
 
 class OneDriveException: Exception
@@ -110,8 +113,8 @@ final class OneDriveApi
 
 		// Configure the User Agent string
 		if (cfg.getValueString("user_agent") == "") {
-			// Application defaults
-			// Comply with traffic decoration requirements
+			// Application User Agent string defaults
+			// Comply with OneDrive traffic decoration requirements
 			// https://docs.microsoft.com/en-us/sharepoint/dev/general-development/how-to-avoid-getting-throttled-or-blocked-in-sharepoint-online
 			// - Identify as ISV and include Company Name, App Name separated by a pipe character and then adding Version number separated with a slash character
 			// Note: If you've created an application, the recommendation is to register and use AppID and AppTitle
@@ -146,6 +149,18 @@ final class OneDriveApi
 
 	bool init()
 	{
+		// Update clientId if application_id is set in config file
+		if (cfg.getValueString("application_id") != "") {
+			// an application_id is set in config file
+			clientId = cfg.getValueString("application_id");
+			companyName = "custom_application";
+		}
+		
+		// detail what we are using for applicaion identification
+		log.vdebug("clientId    = ", clientId);
+		log.vdebug("companyName = ", companyName);
+		log.vdebug("appTitle    = ", appTitle);
+		
 		try {
 			driveId = cfg.getValueString("drive_id");
 			if (driveId.length) {
@@ -188,7 +203,7 @@ final class OneDriveApi
 	{
 		import std.stdio, std.regex;
 		char[] response;
-		string url = authUrl ~ "?client_id=" ~ clientId ~ "&scope=Files.ReadWrite%20Files.ReadWrite.all%20Sites.ReadWrite.All%20offline_access&response_type=code&redirect_uri=" ~ redirectUrl;
+		string url = authUrl ~ "?client_id=" ~ clientId ~ "&scope=Files.ReadWrite%20Files.ReadWrite.all%20Sites.Read.All%20Sites.ReadWrite.All%20offline_access&response_type=code&redirect_uri=" ~ redirectUrl;
 		string authFilesString = cfg.getValueString("auth_files");
 		if (authFilesString == "") {
 			log.log("Authorize this app visiting:\n");
diff --git a/src/sync.d b/src/sync.d
index 80912fce..4d6f149e 100644
--- a/src/sync.d
+++ b/src/sync.d
@@ -290,7 +290,7 @@ final class SyncEngine
 			if (e.httpStatusCode == 401) {
 				// HTTP request returned status code 401 (Unauthorized)
 				log.error("\nERROR: OneDrive returned a 'HTTP 401 Unauthorized' - Cannot Initialize Sync Engine");
-				log.error("ERROR: Check your configuration as your access token may be empty or invalid\n");
+				log.error("ERROR: Check your configuration as your refresh_token may be empty or invalid. You may need to issue a --logout and re-authorise this client.\n");
 				// Must exit here
 				exit(-1);
 			}
@@ -329,7 +329,7 @@ final class SyncEngine
 			if (e.httpStatusCode == 401) {
 				// HTTP request returned status code 401 (Unauthorized)
 				log.error("\nERROR: OneDrive returned a 'HTTP 401 Unauthorized' - Cannot Initialize Sync Engine");
-				log.error("ERROR: Check your configuration as your access token may be empty or invalid\n");
+				log.error("ERROR: Check your configuration as your refresh_token may be empty or invalid. You may need to issue a --logout and re-authorise this client.\n");
 				// Must exit here
 				exit(-1);
 			}