In WHMCS, you can set up credit card expiry notices to remind your clients in advance of their credit card's expiration date. This helps ensure uninterrupted services. Here's how you can do it:

1. Log into WHMCS: Access your WHMCS admin panel using your username and password.

2. Navigate to Configuration: Click on the "Configuration" tab in the top navigation menu.

3. Automation Settings: Under the "System Settings" section, click on "Automation Settings."

4. Credit Card Expiry Notices: In the "Automation Settings" section, scroll down to find the option labeled "Credit Card Expiry Notices."

5. Enable Expiry Notices: Check the box to enable credit card expiry notices.

6. Set Days Before Expiry: Enter the number of days before a credit card's expiry date that you want WHMCS to start sending notices to your clients.

   For example, if you set this to 30 days, WHMCS will start sending notifications one month before the credit card's expiry date.

7. Save Changes: After configuring the credit card expiry notices, click the "Save Changes" button to apply your modifications.

8. Customize Email Templates (Optional): You can customize the email templates for credit card expiry notices by going to "Configuration" > "System Settings" > "Emails." Look for the relevant template named something like "Credit Card Expiry Notice."

   Customize the subject and message of the email to suit your business style and preferences.

Remember to inform your clients in advance about this policy to avoid any surprises. Additionally, it's a good idea to encourage clients to keep their billing information up to date in their client portal.

By enabling credit card expiry notices in WHMCS, you can help ensure that your clients are aware of upcoming expirations and can take the necessary steps to update their payment information.