I am trying to pass 2 object ids to an apex controller in order to use for a SOQL query. I then want to pass the list created in the SOQL query back to the javascript controller. There, I want to see if the list is empty or not and fire a message depending on the result.

component:

<aura:component  implements="flexipage:availableForRecordHome,force:hasRecordId,flexipage:availableForAllPageTypes,force:lightningQuickAction,force:appHostable" controller="getPTM" access="global">
    <aura:attribute name="recordId" type="Id"/>
    <aura:attribute name="plc" type="ts2__Placement__c"/>
    <aura:attribute name="user" type="String"/>
    <aura:attribute name="plan" type="String"/>
     <aura:attribute name="cpaList" type="jstcl__TG_Commission_Plan_Assignment__c[]"/>
    <aura:attribute name="parentId" type="String"/>
    <aura:handler name="init" value="{!this}" action="{!c.doInit}"></aura:handler>
	<aura:handler event="c:selectedsObjectRecordsEvent" action="{!c.submitIt}" />
    <lightning:recordEditForm aura:id="editfrm" recordId="{!v.recordId}" objectApiName="jstcl__PlacementTeamMember__c" onload="{!c.onloadrec}" onsuccess="{!c.successsave}"  > 
        <div class="slds-grid slds-gutters slds-p-horizontal_small">  
            <div class="slds-p-around_xx-small slds-size_2-of-8">   <lightning:inputField aura:id="plc" fieldName="jstcl__Placement__c" value="{!v.parentId}"/></div>
            <div class="slds-p-around_xx-small slds-size_2-of-8">   <lightning:inputField aura:id="user" fieldName="jstcl__User__c" value="{!v.user}"/></div>
            <div class="slds-p-around_xx-small slds-size_2-of-8">   <lightning:inputField aura:id="plan" fieldName="jstcl__CommissionPlan__c" value="{!v.plan}"/></div>
            <div class="slds-p-around_xx-small slds-size_1-of-8">   <lightning:inputField aura:id="split" fieldName="jstcl__SplitPercent__c"/></div>
            <div class="slds-p-around_xx-small slds-size_1-of-8 slds-m-top_large">   <lightning:button variant="brand"
			iconName="utility:add" label="Add User" title="Add User" onclick="{! c.greyOut }" /></div>
        </div>
    </lightning:recordEditForm>
</aura:component>

doInit: function(component, event, helper) {
        //Create the action
       var action = component.get("c.plcGetCPA");
       var user = component.get("v.user");
        var plan = component.get("v.plan");
        action.setParams({
            "user" : user,
            "plan" : plan
        });
        // Add callback behavior for when response is received
        action.setCallback(this, function(response) {
            var state = response.getState();
            if (state === "SUCCESS") {
               component.set("v.cpaList", response.getReturnValue());
            }
            else { console.log("Failed with state: " + state); }
        });
        // Send action off to be executed
        $A.enqueueAction(action);
    },
    greyOut : function(component , event , helper){
        var toastEvent = $A.get("e.force:showToast");
        var user = component.get("v.user");
        var plan = component.get("v.plan");
        var cpaList = component.get("v.cpaList");
		var cpaLength = cpaList.length;
        component.set("v.isOpen", !component.get("v.isOpen"));
        
        if(cpaLength > 0){
        toastEvent.setParams({
            title : 'Success',
            message:'Commission Plan matches.' + cpaList +" -------- "+ plan,
            duration:'5000',
            key: 'info_alt',
            type: 'error',
            mode: 'pester' });
        toastEvent.fire();}   
     else { toastEvent.setParams({
            title : 'Error',
            message:'Commission Plan does not match the user.' + user +' '+ plan,
            duration:'5000',
            key: 'info_alt',
            type: 'error',
            mode: 'pester' });
        toastEvent.fire();}    
    }

public class getPTM {
AuraEnabled
    public static List<jstcl__TG_Commission_Plan_Assignment__c> plcGetCPA(List<Id> userId, List<Id> planId){
       
        List<jstcl__TG_Commission_Plan_Assignment__c> cpaList= new List<jstcl__TG_Commission_Plan_Assignment__c>();
        cpaList = [SELECT Id
                   FROM jstcl__TG_Commission_Plan_Assignment__c 
                   WHERE jstcl__User__r.Id IN :userId AND jstcl__Commission_Plan__r.Id IN :planId];
       
    return cpaList;
        
    }

}