Why is my Stacks transaction pending?

While there are no known issues impacting correct, well-formed transactions, some transactions can be pending for a long time. Pending transactions will be discarded after 256 blocks or ~48 hours — a transaction that is not confirmed, by definition, has no impact on your assets and can be re-sent by the original sender.

More details on transactions in mempool can be found in this forum post on transactions in mempool: best-practices and known issues.