[Apenmeeuw]

i recommend you to use sscanf, it's way better and easier than strtok.

remove all your strtok things from the command and do:

pawn Код:

new targetid;
if(sscanf(params, "u", targetid)) return SendClientMessage(playerid, Red, "[ERROR:]{FFFFFF} /duel [playerid]");

do it like that, also, you need to get the latest sscanf plugin and you need to do

pawn Код:

#include <sscanf2>

for more information about sscanf i suggest you to go to the sscanf topic:
https://sampforum.blast.hk/showthread.php?tid=120356

the download link of sscanf is also there.