[Threshold]

pawn Код:

CMD:blevel(playerid,params[])
{
    new Float:level;
    if(sscanf(params, "f", level)) return SendClientMessage(playerid, COLOR_RED, "USAGE: /blevel [0.0-10.0]");
    PlayerInfo[playerid][Boostlevel] = level;
    return 1;
}

You will need to change 'Boostlevel' in your enum to 'Float:Boostlevel'.