[Calgon]

pawn Код:

CMD:heal(playerid, params[])
{
    SetPlayerHealth(playerid, 99);
    return 1;
}

You added a semi-colon after defining a zcmd command - which is something you can't do. Whenever you begin the code for a function, the parenthesis (brackets) do not require a semi-colon and will generate a compiler error (unless otherwise defined to do so).