Hello,
To automate the process of sending campaigns based on custom field values in WHMCS, you can consider using a third-party marketing automation tool or an email marketing integration with WHCMS that allows conditional logic. Create a custom checkbox field for completed waivers, and integrate it with the marketing tool. Then, set up a campaign with conditions to target clients who purchased products a, b, c but lack products X or addon Y and haven't completed the waiver (based on the custom field value). This will streamline the process, ensuring targeted clients receive reminders until they complete the required waiver.