In order to upload several files at once we need to specify

multiple

attribute and append

[]

to input name

<input type="file" multiple="multiple" name="files[]" placeholder="Attach file"/>

To validate show errors on client side we have to append input name with

.*

Complete example of the

form-group

<div class="form-group">
    <label for="files">Attach File</label> &nbsp;
    <i id="add_new_file" class="ki ki-plus text-success pointer" title="Add New File"></i>
    <input type="file" class="form-control mb-2 {{ $errors->has('files.*') ? 'is-invalid' : '' }}" multiple="multiple" name="files[]" placeholder="Attach file"/>
    @if($errors->has('files.*'))
        <div class="invalid-feedback">
            <strong>{{ $errors->first('files.*') }}</strong>
        </div>
    @endif
</div>

Server side validation of mime types

public function rules()
{
    return [
        'comment' => 'sometimes|nullable|min:2|max:255',
        'files.*' => 'sometimes|nullable|mimes:pdf,docx,xlsx,pptx,rar,zip,png,jpg',
    ];
}

It's necessary the validator key

files

to be appended with the same symbols

.*