No, the title does not say anything ... Explain what the plugin should be. Should it transfer when executing a command? When a player interacts with something? Or what do you mean.
If I use the Slapper command / slapper edit {id} addcommand rca {player} {ip} {port} and I then click on slapper sits there disconnected
I had to fix that issue for a server. It disconnects the player sometimes before the transfer packet seems to take effect. Putting a small delay between transfer packet and closing the player seems to fix the problem.
You can use slapper but you did it wrong, add the command: rca {player} transfer (ip) (port) and there is already a plugin here: https://github.com/Dog2puppy/TransferPE