How to fixed the {variant_id: [{code: “invalid”, message: “is invalid”, options: []} in php

$newrule = (object)[
       "checkout" => (object)[
              "email" => $cEmail,
              "line_items" => [(object)[
                     "variant_id" => "31335443824743",
                     "quantity" => "1"
                ]],
             "shipping_address" => (object)[
                      "first_name" => $firstName,
                      "last_name"  => $lastName,
                      "address1"    => $address1,
                      "city"        => $city,
                      "province_code" => $province_code,
                      "country_code"  => $country_code,
                      "phone" => $phone,
                      "zip" => $zip
                     ]
                  ]    
             ];

Above is my post data that I am sending in my cURL hit. following is my cURL hit.

$access_token_url = "https://" . $query["shop"] . "/admin/api/2020-01/checkouts.json";
                $mycheckOUT = curl_init($access_token_url);
                  curl_setopt($mycheckOUT, CURLOPT_HEADER, FALSE);
                  curl_setopt($mycheckOUT, CURLOPT_ENCODING, 'gzip');
                  curl_setopt($mycheckOUT, CURLOPT_RETURNTRANSFER, TRUE);
                  curl_setopt($mycheckOUT, CURLOPT_FOLLOWLOCATION, TRUE);
                  curl_setopt($mycheckOUT, CURLOPT_MAXREDIRS, 3);
                  curl_setopt($mycheckOUT, CURLOPT_SSL_VERIFYPEER, FALSE);
                  curl_setopt($mycheckOUT, CURLOPT_USERAGENT, 'My New Shopify App v.1');
                  curl_setopt($mycheckOUT, CURLOPT_CONNECTTIMEOUT, 30);
                  curl_setopt($mycheckOUT, CURLOPT_TIMEOUT, 30);
                  curl_setopt($mycheckOUT, CURLOPT_CUSTOMREQUEST, 'POST');
                  // Setup headers
                  $request_headers[] = "X-Shopify-Access-Token: " . $shopData["access_token"];
                  $request_headers[] = 'Content-Type: application/json';
                  $request_headers[] = 'Accept-encoding: charset=utf-8';
                  $request_headers[] = 'Host:'. $query["shop"];
                  
                  curl_setopt($mycheckOUT, CURLOPT_HTTPHEADER, $request_headers);
                  $newrule1   = json_encode($newrule, true);
                  curl_setopt ($mycheckOUT, CURLOPT_POSTFIELDS, $newrule);
                  $resultrule = curl_exec($mycheckOUT);
                  $resultrulea = json_decode($resultrule,true);

Repose of above cURL is given below:

errors: {line_items: [{variant_id: [{code: "invalid", message: "is invalid", options: []}]}]}

Yes, I am trying to pull variants which are exits in my product. see the attached image:

Yes I have tried to pull other variants with same code.
Please check it and help me.