One reason may be yours is a late subscription.
Suppose, your due invoice is on 1st of every month and you subscribed on 5th, usually paypal would send us the payment 4 days late by every month. Since you have not paid on 1st of that month, our system will send you payment reminders to make the payment. You should take care with the subscriptions because if the payment delay exceeds more than 9 days, your account should be suspended until the same has been paid in full settlement with a late fee of $9 USD.
We recommend you to pay before 3 to 4 days of due date to avoid late payments.