How do I remove a stuck Kaspa transaction from a node's mempool?

The only way to remove a stuck RPC-submitted transaction from a Kaspa node's mempool is to restart the node. The mempool is the holding area where unconfirmed transactions wait to be picked up and included in the blockDAG. Transactions submitted through a wallet via RPC never expire on their own — unlike peer-to-peer transactions, which drop off automatically after 60 blocks — so they will keep getting rebroadcast until the node restarts. For most users this means contacting whoever runs the node, but if you run your own Kaspa node you can clear a stuck transaction simply by restarting it.