To add a Voicemail greeting message, follow these steps:

1. Log in to the 3CX Management Console: Open a web browser and enter the URL for your 3CX Management Console. Log in using your administrator credentials. Then click on “Admin”.

2. Navigate to Users: In the management console, go to the "Users" section. This can typically be found in the left-hand menu.

3. Select the User: Locate the User for which you want to set up or change the voicemail greeting. Click on the user to access its settings.

4. Voicemail Greeting: Within the user settings, click on Voicemail.

5. Upload or Record Greeting: You'll have the option to upload an audio file for your voicemail greeting or to record a new one directly through the management console. If you choose to record a new greeting, make sure you have a microphone connected to your computer.

6. Save the Changes: After uploading or recording your voicemail greeting, save the changes.