[RedJohn]

pawn Код:

case 0:
{
    if(GetPlayerMoney(playerid) < 100) return SendClientMessage(playerd, RED, "You don't have enough money!");
    SetPlayerFightingStyle(playerid, FIGHT_STYLE_BOXING);
    GivePlayerMoney(playerid, -100);
    SendClientMessage(playerid, COLOR_WHITE, "You've learnt Boxing!");
}

Or..

pawn Код:

case 0:
{
    if(GetPlayerMoney(playerid) > 100)
    {
        SetPlayerFightingStyle(playerid, FIGHT_STYLE_BOXING);
        GivePlayerMoney(playerid, -100);
        SendClientMessage(playerid, COLOR_WHITE, "You've learnt Boxing!");
    }
    else SendClientMessage(playerd, RED, "You don't have enough money!"); 
}