Use "mimes" when you want to write an extentions (xlsx,doc,docx). In case when use mime-type like application/vnd.ms-excel you must use validation rule mimetype

More mime types: more mime-types

$validator=Validator::make($request->all(),[
 //use this
    'file'=>'required|max:50000|mimes:xlsx,doc,docx,ppt,pptx,ods,odt,odp'
 //or this
    'file'=>'required|max:50000|mimetypes:application/csv,application/excel,
        application/vnd.ms-excel, application/vnd.msexcel,
        text/csv, text/anytext, text/plain, text/x-c,
        text/comma-separated-values,
        inode/x-empty,
        application/vnd.openxmlformats-officedocument.spreadsheetml.sheet'
]

In Laravel you can use validate the file upload with extension using After Hooks. Read more from here!

$validator->after(function ($validator) use ($request){
    if($this->checkExcelFile($request->file('file')->getClientOriginalExtension()) == false) {
        //return validator with error by file input name
        $validator->errors()->add('file', 'The file must be a file of type: csv, xlsx, xls');
    }
});

function checkExcelFile($file_ext){
    $valid=array(
        'csv','xls','xlsx' // add your extensions here.
    );        
    return in_array($file_ext,$valid) ? true : false;
}

First tell that this is not the proper solution. But you can try this.

I've searched also for that and having so much trouble validating excel file and their mimes type is not working for that unfortunately.

if($request->hasFile('file'))
{
   $extension = File::extension($request->file->getClientOriginalName());
   if ($extension == "xlsx" || $extension == "xls" || $extension == "csv") {
      //'Your file is a valid xls or csv file'
   }else {
      //'File is a '.$extension.' file.!! Please upload a valid xls/csv file..!!');
   }
}

in namspace include must use File;

You can validate any file by this way, Thanks.