What it means
The network discarded the transaction, usually because another transaction with the same nonce confirmed first (a speed-up, a cancel, or simply a competing transaction), or because it sat unmined so long the mempool evicted it. A dropped transaction costs nothing: it never executed.
How to fix it
Check the address history on an explorer to see what confirmed in its place. If the action you wanted never happened, submit it again with a market-rate fee.