"Plan Expired" on renewal date is alarming but normal. It accepts payment, continues service without interruption, and fixes itself.
On the plus side, there's no charges at PM when the account is suspended/deactivated or when the account is unsuspended/reactivated. If you do fail to make a payment on time then you just don't get phone service until payment is received - which then starts a new 30-day billing cycle without counting (making you pay for) the days of suspension. Some people deliberately allow their payments and service to lapse into suspension when not using it because travelling/vacation/etc.
An account will remain suspended for 90 days without payment (or autopayment) before it is permanently terminated. So there's no rush if you need time to get stuff straightened out, though it's not prudent to neglect the account until the last few days (just in case any unexpected glitches caused delays).
The downside is that the account needs to be active to collect Rewards. Or to receive notifications from PM about gift offers/etc. If it's suspended when these things are issued then you'll miss out.
