WHMCS does not have a built-in feature that allows you to specify a specific number of weeks to retry a failed payment. However, you can achieve similar behavior by using the "Process Days Before Due" setting and configuring your invoice handling procedures.

Here's how you can set up a retry schedule using this method:

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. Invoice Settings: In the "Automation Settings" section, you'll find various options related to invoicing and billing.

5. Process Days Before Due: Set this to the number of days before an invoice's due date that you want WHMCS to attempt to process the payment. For example, if you want to retry every week, you can set it to 7 days.

   WHMCS will attempt to process the payment this number of days before the invoice's due date.

6. Save Changes: After configuring the "Process Days Before Due" setting, click the "Save Changes" button to apply your modifications.

7. Adjust Invoice Handling:

   • If a payment fails, consider setting the invoice status to "Unpaid" or "Pending" (if it's not already) and notify the client to manually make the payment.

   • You can also set up automated reminder emails to notify clients about unpaid invoices. This can be configured in WHMCS under "Automation Settings."

   • Consider configuring late fee settings to encourage prompt payment.

8. Monitor Payment Logs: Keep an eye on payment logs within WHMCS to track the status of payment attempts. This will help you identify any issues or cases where payments may need manual intervention.

9. Regularly Review and Follow Up: Regularly review the status of invoices and follow up with clients who have outstanding payments.

Remember, while this method allows you to set up a kind of weekly retry schedule, it's important to have manual procedures in place to handle exceptional cases where payments may fail repeatedly. Clear communication with your clients about your payment policies is also crucial.