[Konstantinos]

You are using wrong Callback.
It should be on OnPlayerKeyStateChange(playerid, newkeys, oldkeys)

pawn Код:

#include <a_samp>
#pragma tabsize 0
// PRESSED(keys)
#define PRESSED(%0) \
    (((newkeys & (%0)) == (%0)) && ((oldkeys & (%0)) != (%0)))
// RELEASED(keys)
#define RELEASED(%0) \
    (((newkeys & (%0)) != (%0)) && ((oldkeys & (%0)) == (%0)))
// PRESSED(keys)
#define PRESSED(%0) \
    (((newkeys & (%0)) == (%0)) && ((oldkeys & (%0)) != (%0)))
//-------------------------------------------------

public OnFilterScriptInit()
{
    return 1;
}
//-------------------------------------------------

public OnPlayerKeyStateChange(playerid, newkeys, oldkeys)
{
    if(PRESSED(KEY_ACTION)) {
        if(IsPlayerInAnyVehicle(playerid)) {
            new vehid = GetPlayerVehicleID(playerid);
            // warning 204: symbol is assigned a value that is never used: "vehid"
            // You have to use it somewhere and it will compile without warnings too as without errors.
            for(new i = 0; i<MAX_PLAYERS; i++) {
                // Code Here
            }
        }
        else if(RELEASED(KEY_ACTION)) {
                // Code Here
        }
    }
    return 1;
}
//-------------------------------------------------

public OnPlayerUpdate(playerid)
{
    if(!IsPlayerConnected(playerid)) return 0;
    if(IsPlayerNPC(playerid)) return 1;

    // Handle playing SomaFM at the alhambra
    if(GetPlayerInterior(playerid) == 17) {
        if(IsPlayerInRangeOfPoint(playerid,70.0,489.5824,-14.7563,1000.6797)) { // alhambra middle
            if(!GetPVarInt(playerid,"alhambra")) {
                SetPVarInt(playerid,"alhambra",1);
                PlayAudioStreamForPlayer(playerid, "http://somafm.com/tags.pls",480.9575,-3.5402,1002.0781,40.0,true);
            }
        }
    }
    else {
        if(GetPVarInt(playerid,"alhambra")) {
            DeletePVar(playerid,"alhambra");
            StopAudioStreamForPlayer(playerid);
        }
    }

    return 1;
}

//-------------------------------------------------