$end = Requests::where('confirmed_walker', $rid) ->orderBy('id', 'desc') ->first();

i'm fresher for laravel and i don'y know where is the error in my code.Here, if i write $rid it will not work bt if i replace '$rid' with number like 106,1,2 it will work. can anyone plaese tell me where is error

$end = Requests::where('confirmed_walker', $rid)
       ->orderBy('id', 'desc')
       ->first();

via Chebli Mohamed