So I've been coding a little idle game, and I have a few buttons which are for upgrades. I had 3 before, and when i added the fourth one, for some reason it isn't working properly.

JavaScript:

```
gainUpgrade: function() {
    if (engine.player.Energy >= engine.idleGainUpgrade) {
        engine.player.Energy -= engine.idleGainUpgrade;
        engine.idleGain += 0.5;
        engine.display.Energy.innerHTML = engine.player.Energy;
        engine.display.idleGain.innerHTML = engine.idleGain;
        engine.Status("Upgrade unlocked!");
        engine.idleGainUpgrade += (engine.idleGainPriceMultiplier * 50 * 2);
        engine.display.idleGainUpgrade.innerHTML = engine.idleGainUpgrade;
        engine.idleGainPriceMultiplier +=0.5;
    } else {
        engine.Status("Not enough energy!");
    }
},

```

That's the function that is linked the with the button, the JavaScript that should trigger it is:

```
engine.clickables.gainUpgrade = document.getElementById("idlegainupgrade");
engine.clickables.gainUpgrade.addEventListener("click", function() {
    engine.gainUpgrade;
});

```

And the HTML bit of code:

```
<input type="button" id="idlegainupgrade" value="Increase gain from idle!"><br /><br />
<h6>
    Idle Gain: <span id="idlegain"></span>
    <br />Idle Gain Upgrade Cost: <span id="idlegainupgradecost"></span>
</h6>

```

What have I done wrong?