#define MAX_PACKAGES 20
#define DIALOG_BUY_PACKAGE 1

enum PackInfo
{
    PackNumber[5], // Length of package number will be 5 as you said for ex. 13546 or 35464 or 53634
    PackPrice //You ccould just not use this , its for ex.
}
new PackageInfo[MAX_PACKAGES][PackInfo];

CMD:buypackage(playerid,params[])
{
    if(IsPlayerInRangeOfPoint(playerid, 3, x, y, z)) // the position where player should be
    {
        ShowPlayerDialog(playerid, DIALOG_BUY_PACKAGE, DIALOG_STYLE_INPUT, "Buy package", "Please enter the number of the package", "OK", "Cancel");
    }
    return 1;
}


public OnDialogResponse(playerid, dialogid, response, listitem, inputtext[])
{
    switch(dialogid)
    {
        case DIALOG_BUY_PACKAGE:
        {
            if(response)
            {
                if(!IsNumeric(inputtext)) return ShowPlayerDialog(playerid, DIALOG_BUY_PACKAGE, DIALOG_STYLE_INPUT, "Buy package", "You can only write numbers!\nPlease enter the number of the package", "OK", "Cancel");
                for(new p;p < MAX_PACKAGES;p++)
                {
                    if(strval(inputtext) == PackageInfo[p][PackNumber] && GetPlayerMoney(playerid) > PackageInfo[p][PackPrice])
                    {
                        //Do your desired actions here
                    }
                }
            }
        }
    }
    return 1;
}

IsNumeric(const string[])
{
    for (new i = 0, j = strlen(string); i < j; i++)
    {
        if (string[i] > '9' || string[i] < '0') return 0;
    }
    return 1;
}