It should also be able to check if the subscription is still active before sending a reminder.

Also, trigger email and SMS reminders.

This is a must as we have been dealing with refunds and chargebacks because they were not notified before the current billing cycle ends.

100% need to remind people of a charge before it happens. And not just charges through highlevel but charges via external payments systems too. Should be able to have a field called day of month and send them a text message reminder 2 days before that they are going to be billed.

Totally agree. Would love to be able to notify clients about an upcoming charge before it happens. Adds a sort of trust-factor with clients.