explode to add checkboxes dynamically

I am trying to get array of checkbox from database and then explode them to check each checkbox dynamically but the results

getting all checkbox not checked, however if I try {!! diploma->courses !!} the results will be (2,3,7).

Any help please what I am missing here.

Here is the controller

public function edit( $id ) {
        $diploma          = Diploma::query()->find( $id );
        $courseCategories = CourseCategory::all();

        return view( 'admin.diploma.edit', compact( 'diploma', 'courseCategories' ) );
    }

and here is where it should explode the checkbox

<div class="box-group" id="accordion">
    
    <?php $i = 1; ?>
    @foreach($courseCategories as $courseCategory)
        <?php $i ++ ?>
        <div class="panel box box-primary">
            <div class="box-header with-border">
                <h4 class="box-title">
                    <a data-toggle="collapse" data-parent="#accordion"
                       href="#collapse{!! $i !!}"
                       aria-expanded="false" class="collapsed">
                        {!! $courseCategory->title !!}
                    </a>
                </h4>
            </div>
            <div id="collapse{!! $i !!}" class="panel-collapse collapse" aria-expanded="false"
                 style="height: 0;">
                <div class="box-body">
                    <div class="form-group">
                        @foreach($courseCategory->courseItem as $course)
                            <div class="checkbox">
                                <label>
                                    <input type="checkbox" name="courses[]"
                                           value="{!! $course->id !!}"
                                            {!! in_array($course->id, explode(",", $diploma->coueses)) ? 'checked' : '' !!} >
                                    {!! $course->title !!}
                                </label>
                            </div>
                        @endforeach
                    </div>
                </div>
            </div>
        </div>
@endforeach
</div>