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I want to update the PO number of my customer whenever he renews his account. How to get notified on this?
In Chargebee, you can get notified on the subscription renewals using webhooks or reminder emails.
To get notified of subscription-related events, refer to this article. You can use any one of the notifications/webhooks.
Using Subscription Renewal Reminder
Add your email as CC/BCC when you set Subscription Renewal Reminders under Settings > Configure Chargebee > Email notifications to notify yourself along with your customers (n) days before their renewal.
Info: You can also set up Email segmentation if you want to notify only a specific set of customers.
Related articles and Documentation
How can I be notified of only certain events using webhooks?