The reminder emails could not contains invoice. You are using offline payments for these recurring subscriptions, correct?
If Yes, please enable the plugin System - Membership Pro Offline Recurring Invoice . The system will then send an email with invoice certain number of days before subscription expired to subscribers so that they can make payment. You can go to Membership Pro -> Emails & Messages, look at Recurring Subscription Messages tab, find the following items and change it to meet your need:
- Offline Recurring Email Subject
- Offline Recurring Email Body
Please try that and let us know if you have any other questions