Step 1: Go to the TMS URL: 

Step 2: Choose the correct account

Step 3: Click on the TMS User menu item.

Step 4: Click on the Manager sub-menu item.

Step 5: Click on “Create Extension”.

Step 6: Select an extension type.

Step 7: Give the extension a number - This should follow the previously created number. 

Step 8: Click” Add Extension” to save the extension. 

Note: A notification will open to inform you that the extension will be added to your next billing run.