[Calgon]

Your code is a horrible mess. Furthermore, you don't need an IPC check, the player is connected to have used the command.

pawn Код:

COMMAND:clantag(playerid, params[]) { // If you're using zcmd, you don't need 'cmdtext[]'
    if(!isnull(params)) {
        // The command contains a string that we can parse just by 'params'
        new
            playerClanTagandName[MAX_PLAYER_NAME], // For formatting the new player name 
            playerName[MAX_PLAYER_NAME]; // Use the define/constant. It's 24, not 256.

        GetPlayerName(playerid, playerName, MAX_PLAYER_NAME); // Getting the players name. 
        
        format(playerClanTagandName, MAX_PLAYER_NAME, "[%s]%s", params, playerName); // Formatting
        SetPlayerName(playerid, playerClanTagandName); // Setting the new name
    }
}

I assume that's what you originally wanted, it'd get the old name, put the clan tag in front, then change their name to it.