If you know the reason for expiry, like "card failure/decline" or "invoice overdue" etc., you can use:
"Your Subscription has expired due to <reason>. Click here to sign up to renew".
Don't try to make it fancy. Also, don't wait 90 days. Send 5 emails for renewal, starting with 10 days before renewal as a heads up in case people want to update their card on file. Then on the day of if it fails, you can try upto 3 more times and for each failure notify the customer. After the 3 attempts, you can stop the service and manually reach out over email to someone and then do another 3 follow-ups while the service remains suspended.