[SalesForce] Aura – Unable to find action on the controller in Lightning Components

I've been dabbling around Lightning Components (Aura). I decided to use Aura so I can display may Lightning Web Component (LWC) in a pop-up window (or modal) through the click of a Custom Quick Action. However, I keep getting an error.

Basically, all I'm trying to accomplish with Aura is to:

1. Fetch the Stage__c field by calling an Apex method.
2. Check if that Stage__c's field value is equal or not equal to "Closed".
3. Display a toast message and close the component if Stage__c == "Closed", in succession.

I've written a simple code to do this but I can't seem to move forward and call the Apex correctly as I'm always receiving this error:

So, I checked my Apex method to make sure it has @AuraEnabled annotation, but to no avail.

Here's what I have:

CMP

<aura:component implements="force:lightningQuickActionWithoutHeader,force:hasRecordId" >
    <aura:attribute name="recordId" type="Id" />
    <aura:handler name="init" value="{!this}" action="{!c.doInit}" /> 
    <c:editProduct recordId="{!v.recordId}" onclose="{!c.closeQA}"/>
</aura:component>

Controller JS

({ doInit : function(component, event, helper){
        helper.getOppty(component);
    }
})

Helper JS

({ 
getOppty : function(component, event, helper) {
    var action = component.get("c.getOpptyCurrency");
    action.setParams({
        opptyId: component.get("v.recordId")
    });
    action.setCallback(this, function(a){
        var state = a.getState();
        var returnVal = a.getReturnValue();
        console.log('Return Value :', returnVal);

        if(state == "SUCCESS"){
            for(i=0; i < returnVal.length; i++){
                var stage = returnVal[i];
                stage.Stage__c;
            }
        }else{
            console.log("Failed with state: " + state);
        }
    });
    $A.enqueueAction(action);

    console.log('Stage :', stage.Stage__c);
    if(stage.Stage__c === "Closed"){
        this.closeQA(component, event, helper);
        this.showError(component, event, helper);
    }
},

showError : function(component, event, helper) {
        var toastEvent = $A.get("e.force:showToast");
        toastEvent.setParams({
            title : 'Error',
            message:'This is an error message',
            duration:' 5000',
            key: 'info_alt',
            type: 'error',
            mode: 'dismissible'
        });
        toastEvent.fire();
    },

closeQA : function(component, event, helper) {
        $A.get("e.force:closeQuickAction").fire();
    }
})

Apex

@AuraEnabled
public static Opportunity__c getOpptyCurrency(string opptyId){
        Opportunity__c oppty = [SELECT Id, Stage__c
                                FROM Opportunity__c
                                WHERE Id =: opptyId LIMIT 1];
        return oppty;
     }

Can anyone help point me in the right direction? What am I doing wrong exactly in this case