guzzlehttp throwing error on laravel project - strtolower(): Argument #1 ($string) must be of type string, int given

I am trying to consume one POST api using guzzlehttp In my laravel project. But i am getting one error on my dev server. This working perfectly on my local system. $postArray is manipulating correctly both side. This is my composer version. "guzzlehttp/guzzle": "^7.3", If any one know about this please help me out.

     $response = Http::withHeaders([
            "accept: application/json",
            "content-type: application/json"
        ])->post('https://staging.consume.com/testing', $postArray)->json();

strtolower(): Argument #1 ($string) must be of type string, int given

    {
"message": "strtolower(): Argument #1 ($string) must be of type string, int given",
"exception": "TypeError",
"file": "/mnt/drive_1/www/deploy-api-2021-07-29-14-25-12/vendor/guzzlehttp/psr7/src/Utils.php",
"line": 28,
"trace": [
    {
        "file": "/mnt/drive_1/www/deploy-api-2021-07-29-14-25-12/vendor/guzzlehttp/psr7/src/Utils.php",
        "line": 28,
        "function": "strtolower"
    },
    {
        "file": "/mnt/drive_1/www/deploy-api-2021-07-29-14-25-12/vendor/guzzlehttp/psr7/src/Utils.php",
        "line": 189,
        "function": "caselessRemove",
        "class": "GuzzleHttp\\Psr7\\Utils",
        "type": "::"
    },
    {
        "file": "/mnt/drive_1/www/deploy-api-2021-07-29-14-25-12/vendor/guzzlehttp/guzzle/src/Client.php",
        "line": 455,
        "function": "modifyRequest",
        "class": "GuzzleHttp\\Psr7\\Utils",
        "type": "::"
    },

source https://stackoverflow.com/questions/68581387/guzzlehttp-throwing-error-on-laravel-project-strtolower-argument-1-strin