I have a lightning component which is used to merge the custom lead object which is a duplicate. Here, I have a requirement that if the two selected leads are marked as true for Integrated_Lead__c field, then when clicked on merge, an error should be displayed on the page that "Leads cannot be merged".

Below is my Apex Class method:
 

@auraEnabled
public Static List<cContact> contactsearch(String userinp, String userinput) {
    system.debug(userinput + '=======' + userinp);
    errormsg = false;
    errormsg2 = false;
    contactList = new List<cContact>();
    String query;
    String leadName;
    if (!String.isEmpty(userinp)) {
        leadName = userinp + '%' + userinput + '%';
        system.debug('if====' + leadName);
    } else {
        leadName = '%' + userinput + '%';
        system.debug('else====' + leadName);
    }
    system.debug('leadName===>' + leadName);
    
        for (Lead_Custom__c c : [select Name, First_Name__c, Last_Name__c, Integrated_Lead__c, Id, Cell_Phone__c, Mailing_Street__c, Mailing_City__c, Mailing_State_Province__c from Lead_Custom__c where Name like :leadName]) {
            contactList.add(new cContact(c));
        }
    
    return contactList;
}
@auraEnabled
public Static List<cContact> getresults() {
    return contactList;
}

Lightning Component:
 

<aura:component controller="SearchDuplicateLeads_Lightning" implements="force:appHostable,flexipage:availableForAllPageTypes" access="global">
  
    <aura:handler name="init" value="{!this}" action="{!c.SearchDuplicateLeads}"/>
    <aura:attribute name="userinput" type="String" default=""/>
    <aura:attribute name="userinp" type="String" default=""/>
    <aura:attribute name="render" type="Boolean" default="false"/>
    <aura:attribute name="Spinner" type="boolean" default="false"/>
    
    <aura:attribute name="contactList" type="String[]" />
   
                                <aura:iteration items="{!v.contactList}" var="contacts">
                                    <tr class="slds-hint-parent">
                                        <td role="gridcell" class="mycol">
                                            <lightning:input type="checkbox" aura:id="selected" label=" " value="{!contacts.selected}" onchange="{!c.singleChecked}"/>
                                        </td>
                                        <td role="gridcell">
                                            <ui:outputText value="{!contacts.con.Name}" />
                                        </td>
                                        
                                    </tr>
                                </aura:iteration>
                                </tbody>
                            </table>
                        </div>
                        <lightning:button variant="brand" onclick="{!c.processrecSelected}" label="Next" class="cus-button"/>
                        <lightning:button variant="brand" onclick="{!c.Cancel}" label="Cancel" class="cus-button"/>
                    </aura:renderIf>
                </div>
            </div>
        </div>
    </div>
</aura:component>

Js:
 

processrecSelected: function(component, event, helper) {
    var action = component.get('c.processSelected');
    var strData = JSON.stringify(component.get('v.contactList'));
    console.log('strData===>'+strData);
    action.setParams({ 'contactstr' : strData});
    action.setCallback(this,function(response){
        if (response.getState() === "SUCCESS") {
            var res = response.getReturnValue();
            console.log('res===>'+res.length);
            if(res.length==2){
                redirecttoMerge(res[0].Id,res[1].Id);
            }else if(res.length>2){
                toastEvt('Please select at most two records to proceed');
            }else if(res.length==1){
                toastEvt('Please select at most two records to proceed');
            }else{
                toastEvt('Please select a record to proceed.');
            }
        }
    })
    $A.enqueueAction(action);
    function toastEvt(msg){
        var toastEvent = $A.get("e.force:showToast");
        toastEvent.setParams({
            "title": "Error!",
            "type":"Error",
            "message": msg
        });
        toastEvent.fire();
    }
},

Now, from the above contactList, the merging will be done when two Custom Leads are selected. As per my requirement, if the selected two leads are having Integrated_Lead__c = True, then an error message should be displayed on the screen that "Leads cannot be merged" on click on next button.
​​​​​​​
Can anyone please suggest the changes so that I can get the error message displayed on screen