How to Activate Windows 11 & Windows 10 by Phone (slui 4, slmgr.vbs & Free GetCID)

1. Why Does Windows Ask for Telephone Activation (Error 0xC004C008)?

When you enter a genuine Retail, OEM, or Volume MAK product key in Windows 11 or Windows 10, Microsoft's online activation servers check the key's hardware binding history. In several common scenarios, Windows will decline direct one-click internet activation and display error code 0xC004C008 ("The activation server determined that the specified product key could not be used") or 0xC004C020:

• Motherboard / Hardware Upgrade or Reinstall: You reinstalled Windows 11/10 on the same PC or transferred a Retail license to a new computer, triggering Microsoft's automated phone verification check.
• OEM System Builder & Retail Keys with Phone Eligibility: Many genuine Retail and OEM (`OEM:NONSLP` / `OEM:DM`) product keys require a one-time Confirmation ID (CID) handshake to complete activation.
• Offline or Air-Gapped Workstations: Computers without direct access to Microsoft's internet licensing endpoints can be permanently activated using a 63-digit Installation ID (IID) and 48-digit Confirmation ID (CID).

2. Method 1: Activate Windows 11 & 10 Using the slui 4 Activation Wizard

The built-in Windows Telephone Activation Wizard (slui.exe 4) is the easiest graphical way to obtain your 63-digit Installation ID and enter your 48-digit Confirmation ID.

Step 1: Install Your Product Key in Windows

Open Settings → System → Activation → Change product key and enter your 25-character Windows 11 or Windows 10 key. Alternatively, open Command Prompt as Administrator and run:

slmgr.vbs /ipk XXXXX-XXXXX-XXXXX-XXXXX-XXXXX

Step 2: Launch the Telephone Activation Window (slui 4)

1. Press Win + R on your keyboard to open the Run dialog box.
2. Type slui 4 and press Enter (or click OK).
3. Select any country or region from the dropdown list and click Next.
4. Look at Step 2 on the screen: Windows will display 9 groups of 7 digits (63 digits in total). This is your Installation ID (IID).

Step 3: Generate Your Free 48-Digit Confirmation ID on GetCID.cc

Instead of calling Microsoft's automated toll-free phone line and spending 10 minutes reading 63 digits over the keypad, paste your Installation ID directly into our Free GetCID Generator:

Step 4: Enter Confirmation ID Blocks A through H

Click Enter Confirmation ID in the slui 4 window, type or paste the 8 generated 6-digit blocks (Block A through Block H), and click Activate Windows. Your Windows 11 or Windows 10 system is now permanently activated with a digital entitlement!

3. Method 2: Activate via Command Prompt (Fix when slui 4 Does Not Open)

On newer builds of Windows 11 (23H2 and 24H2), typing slui 4 sometimes does nothing or fails to open the graphical wizard. You can perform the entire telephone activation process in 30 seconds using slmgr.vbs in an elevated Command Prompt or PowerShell window:

Step 1: Open Command Prompt as Administrator

Click the Start menu, type cmd, right-click Command Prompt, and select Run as administrator.

Step 2: Install Your Windows Product Key

cscript //nologo %windir%\system32\slmgr.vbs /ipk XXXXX-XXXXX-XXXXX-XXXXX-XXXXX

Step 3: Display Your 63-Digit Installation ID (IID)

Run the following command to output your 63-digit Installation ID directly in the terminal:

cscript //nologo %windir%\system32\slmgr.vbs /dti

Copy the 63-digit number printed after Installation ID: and paste it into GetCID.cc to get your 48-digit Confirmation ID.

Step 4: Apply the 48-Digit Confirmation ID & Activate

Copy the continuous 48-digit Confirmation ID (without dashes) from GetCID.cc and run these two commands:

cscript //nologo %windir%\system32\slmgr.vbs /atp YOUR_48_DIGIT_CONFIRMATION_ID
cscript //nologo %windir%\system32\slmgr.vbs /ato

Step 5: Verify Permanent Activation Status

slmgr.vbs /xpr

A pop-up window will confirm: "The machine is permanently activated."

4. Troubleshooting Windows Phone Activation Errors