angular – Adding Chevron icon to ngx-bootsrap accordion

I have a problem changing the chevron from UP to DOWN when clicking the accordion. It seems to always result to true no matter what trick I tried and even tried other examples like this

        <accordion [closeOthers]="true">
                <accordion-group #group [isOpen]='true'>
                    <div accordion-heading class="clearfix">
                        Basic Information
                        <span class="badge badge-secondary float-right pull-right">
                            <i class="fa" [ngClass]="!group?.isOpen ? 'fa-chevron-down': 'fa-chevron-down'"></i>

لینک منبع