if(GetDistanceBetweenPlayers(playerid,ID) > 5)
    {
        format(string,sizeof(string),"%s(%d) is too far away. You cannot reach him to rob him.",PlayerName(ID),ID);
        SendClientMessage(playerid,COLOR_RED_ERROR,string);
        return 1;
    }

CMD:rob(playerid,params[])
{
    new string[128];
    new ID;
    if(sscanf(params, "u", ID))
    {
        SendClientMessage(playerid,COLOR_RED_ERROR,"Usage: /rob (Player Name/ID)");
        return 1;
    }
    if(IsCuffed[playerid] == 1)
    {
        SendClientMessage(playerid,COLOR_RED_ERROR,"You cannot use this command while your cuffed");
        return 1;
    }
    if(JailTime[playerid] >= 1)
    {
        SendClientMessage(playerid, COLOR_RED_ERROR, "You are in jail! you cant rob someone");
        return 1;
    }
    if(IsSpawned[playerid] != 1)
    {
        SendClientMessage(playerid,COLOR_RED_ERROR,"You must be alive and spawned in order to be able to use this command.");
        return 1;
    }
    if(IsFrozen[playerid] == 1)
    {
        SendClientMessage(playerid,COLOR_RED_ERROR,"You have been frozen by a Server Administrator. You cannot use this command.");
        return 1;
    }
    if(InAdminMode[ID] == 1)
    {
        SendClientMessage(playerid,COLOR_RED_ERROR,"You cannot use this command on this player because they are in Administrator mode.");
        return 1;
    }
    if(IsKidnapped[playerid] == 1)
    {
        SendClientMessage(playerid,COLOR_RED_ERROR,"You are kidnapped. You cannot use this command.");
        return 1;
    }
    if(gTeam[playerid] == TEAM_POLICE || gTeam[playerid] == TEAM_ARMY || gTeam[playerid] == TEAM_CIA)
    {
        SendClientMessage(playerid,COLOR_RED_ERROR,"You cannot rob players with your class/skill.");
        return 1;
    }
    if(!IsPlayerConnected(ID))
    {
        format(string,sizeof(string),"The player ID (%d) is not connected to the server. You cannot rob them",ID);
        SendClientMessage(playerid,COLOR_RED_ERROR,string);
        return 1;
    }
    if(GetDistanceBetweenPlayers(playerid,ID) > 5)
    {
        format(string,sizeof(string),"%s(%d) is too far away. You cannot reach him to rob him.",PlayerName(ID),ID);
        SendClientMessage(playerid,COLOR_RED_ERROR,string);
        return 1;
    }
    if(GetPlayerState(playerid) == PLAYER_STATE_DRIVER || GetPlayerState(playerid) == PLAYER_STATE_PASSENGER)
    {
        SendClientMessage(playerid,COLOR_RED_ERROR,"You cannot rob someone while in a vehicle. Exit the vehicle first.");
        return 1;
    }
    if(GetPlayerState(ID) == PLAYER_STATE_DRIVER || GetPlayerState(ID) == PLAYER_STATE_PASSENGER)
    {
        SendClientMessage(playerid,COLOR_RED_ERROR,"You cannot rob someone while they are in a vehicle. Get them to exit the vehicle first.");
        return 1;
    }
    if(playerid == ID)
    {
        SendClientMessage(playerid,COLOR_RED_ERROR,"You cannot rob yourself, how can you even manage that?");
        return 1;
    }
    if(IsSpawned[ID] != 1)
    {
        format(string,sizeof(string),"%s(%d) is not spawned. You cannot rob dead people ..",PlayerName(ID),ID);
        SendClientMessage(playerid,COLOR_RED_ERROR,string);
        return 1;
    }
    if(IsFrozen[ID] == 1)
    {
        format(string,sizeof(string),"%s(%d) is frozen by a Server Administrator. You cannot rob them.",PlayerName(ID),ID);
        SendClientMessage(playerid,COLOR_RED_ERROR,string);
        return 1;
    }
    if(AttemptedToRobRecently[playerid] >= 1)
    {
        SendClientMessage(playerid,COLOR_RED_ERROR,"You are too tired from your last rob attempt. Please wait before robbing again.");
        return 1;
    }
    if(HasRobbedRecently[playerid] >= 1)
    {
        SendClientMessage(playerid,COLOR_RED_ERROR,"You are too tired from the last person you robbed. Please wait before robbing again.");
        return 1;
    }
    if(GetPlayerMoney(ID) <= 0)
    {
        SendClientMessage(playerid,COLOR_RED_ERROR,"That player has no money in their pockets. What would be the point in robbing them?");
        return 1;
    }
    new crand = random(100);
    if(crand <= 30)
    {
        SendClientMessage(playerid,COLOR_RED_ERROR,"Rob attempt failed. The player slipped out of your grasp.");
        AttemptedToRobRecently[playerid] =35;
        return 1;
    }
    if(HasSecureWallet[ID] > 1)
    {
        SendClientMessage(playerid,COLOR_RED_ERROR,"You cant rob this person. He have security wallet.");
        HasSecureWallet[ID] = HasSecureWallet[ID] - 1;
        format(string, sizeof(string), "%s has attempted to rob you, you now have %d security wallet left.", PlayerName(playerid),HasSecureWallet[ID]);
        SendClientMessage(ID, -1, string);
        HasRobbedRecently[playerid] =180;
        return 1;
    }
    if(GetDistanceBetweenPlayers(playerid,ID) <= 5 && crand > 30)
    {
        new current_zone = player_zone[playerid];
        new mrand =random(GetPlayerMoney(ID));
        SendClientMessage(playerid,COLOR_GREY,"[[_Player Robbed_]]");
        format(string,sizeof(string),"You have robbed $%d from %s(%d). Careful they dont come after you!",mrand,PlayerName(ID),ID);
        SendClientMessage(playerid,COLOR_RED,string);
        GivePlayerMoney(playerid,mrand);
        IncreaseWantedLevel(playerid,8);
        HasRobbedRecently[playerid] =180;
        IncreasePlayerScore(playerid,3);

        SendClientMessage(ID,COLOR_GREY,"[[_Robbed_]]");
        format(string,sizeof(string),"You have had $%d robbed from you by %s(%d). Kill them for your money back or run!",mrand,PlayerName(playerid),playerid);
        SendClientMessage(ID,COLOR_RED,string);
        GivePlayerMoney(ID,-mrand);

        format(string,sizeof(string),"[DISPATCH] Robbery: %s(%d) has robbed $%d from %s(%d). Location: %s.",PlayerName(playerid),playerid,mrand,PlayerName(ID),ID,zones[current_zone][zone_name]);
        SendClientMessageToAllCops(string);
        return 1;
    }
    return 1;
}

forward Float:GetDistanceBetweenPlayers(p1,p2);
public Float:GetDistanceBetweenPlayers(p1,p2)
{
    new /*Float:x1,Float:y1,Float:z1,*/Float:x2,Float:y2,Float:z2;
    /*if (!IsPlayerConnected(p1) || !IsPlayerConnected(p2))
    {
        return -1.00;
    }
    GetPlayerPos(p1,x1,y1,z1);
    GetPlayerPos(p2,x2,y2,z2);
    return floatsqroot(floatpower(floatabs(floatsub(x2,x1)),2)+floatpower(floatabs(floatsub(y2,y1)),2)+floatpower(floatabs(floatsub(z2,z1)),2));*/
    //GetPlayerPos(p1, x1, y1, z1);
    GetPlayerPos(p2, x2, y2, z2);
    return GetPlayerDistanceFromPoint(p1, x2, y2, z2);
}

//...
if(!IsPlayerConnected(ID))
{
    format(string,sizeof(string),"The player ID (%d) is not connected to the server. You cannot rob them",ID);
    SendClientMessage(playerid,COLOR_RED_ERROR,string);
    return 1;
}
new Float:A[3];
GetPlayerPos(ID,A[0],A[1],A[2]);
if(IsPlayerInRangeOfPoint(playerid,5.0,A[0],A[1],A[2]))
{
    format(string,sizeof(string),"%s(%d) is too far away. You cannot reach him to rob him.",PlayerName(ID),ID);
    SendClientMessage(playerid,COLOR_RED_ERROR,string);
    return 1;
}

forward GetDistanceBetweenPlayers(p1, p2);
public GetDistanceBetweenPlayers(p1, p2)
{
    new Float:x2,Float:y2,Float:z2; new Float:x1,Float:y1,Float:z1;
    if (!IsPlayerConnected(p1) || !IsPlayerConnected(p2))
    {
        return -1.00;
    }
    GetPlayerPos(p1,x1,y1,z1);
    GetPlayerPos(p2,x2,y2,z2);
    return GetPlayerDistanceFromPoint(p1, x2, y2, z2);
}
The best way to debug is to use a make do command like /showdistance to verify if the function works.

forward GetDistanceBetweenPlayers(p1, p2);
public GetDistanceBetweenPlayers(p1, p2)
{
    new Float:x2,Float:y2,Float:z2; new Float:x1,Float:y1,Float:z1;
    if (!IsPlayerConnected(p1) || !IsPlayerConnected(p2))
    {
        return -1.00;
    }
    GetPlayerPos(p1,x1,y1,z1);
    GetPlayerPos(p2,x2,y2,z2);
    new Float:distance = GetPlayerDistanceFromPoint(p1, x2, y2, z2);
    return distance;
}

forward GetDistanceBetweenPlayers(p1, p2);
public GetDistanceBetweenPlayers(p1, p2)
{
    new Float:x2,Float:y2,Float:z2; new Float:x1,Float:y1,Float:z1;
    if (!IsPlayerConnected(p1) || !IsPlayerConnected(p2))
    {
        return -1.00;//Warning line
    }
    GetPlayerPos(p1,x1,y1,z1);
    GetPlayerPos(p2,x2,y2,z2);
    new Float:distance = GetPlayerDistanceFromPoint(p1, x2, y2, z2);
    return distance;//Warning line
}

forward GetDistanceBetweenPlayers(p1, p2);
public GetDistanceBetweenPlayers(p1, p2)
{
    new Float:x2,Float:y2,Float:z2; new Float:x1,Float:y1,Float:z1;
    if (!IsPlayerConnected(p1) || !IsPlayerConnected(p2)) return 0;
    GetPlayerPos(p1,x1,y1,z1);
    GetPlayerPos(p2,x2,y2,z2);
    new Float:distance = GetPlayerDistanceFromPoint(p1, x2, y2, z2);
    return distance;
}

forward Float:GetDistanceBetweenPlayers(p1, p2);
public Float:GetDistanceBetweenPlayers(p1, p2)
{
    new Float:x2,Float:y2,Float:z2;
    if (!IsPlayerConnected(p1) || !IsPlayerConnected(p2)) return -1.0;
    GetPlayerPos(p2,x2,y2,z2);
    new Float:distance = GetPlayerDistanceFromPoint(p1, x2, y2, z2);
    return distance;
}