Is there a statute of limits on debit card transactions posting? We have a customer who used their debit card to purchase an item in September 2017 and the item is trying to post today. Any insight would be appreciated.

There is no "stale dated" debit card transaction like these is a stale dated check. VISA/MC rules both require the issuer to attempt to post all transactions. In the event that you are unable to post a transaction because the account is now overdrawn or closed you may have "Late Presentment" chargeback rights.

For VISA a transaction is considered late if the acquirer settles more than 30 days from the authorization date and 7 days for MC. Note that the authorization date for Travel and Entertainment purchases such as hotel stays, rental cars and cruises is the date the services are completed, car returned, etc.