Guzzle 6 PUT returning 400 error but works fine in SOAP UI

I am trying to work out why a Guzzle PUT request, in a Laravel 5 application, I am making is returning a 400 error when the same request works fine in SoapUI. I am trying to send a JSON string to an API with a PUT.

I am having no trouble getting data from this API it is putting the JSON body I am having trouble with.

The $base_api variable is the base url of the API server.

The $uri = 'refData/dropRoutes/'; and this is the particular endpoint I am trying to post the JSON body to.

Here is my code for setting up the Client

$client = new Client([
        'base_uri' => $base_api,
        'timeout'  => 10.0,
        'proxy' => ['no' => ['.casino.internal']],
        'verify' => false,
        'headers' => [
            'Accept' => 'application/json',
            'Accept-Encoding' => 'gzip,deflate',
            'tseg-user' => $_COOKIE['egmtool_name'],
            'tseg-source' => 'Drop Collection Tool',
            'tseg-host' => request()->ip(),
            'tseg-context' => '',
            'tseg-datetime' => Date('d-m-Y H:i:s' ),
            'tseg-property' => $location
        ],
    ]);

Here is the request I am trying

$response = $client->request(
        'PUT',
        $uri,
        ['debug' => fopen('C:\\xampp\\htdocs\\egmbank\\storage\\logs\\log2.txt','a+')],
        ['auth' => [config('app.api_username'), config('app.api_password')]],
        ['json' => $json_body]

    );

I have copied the JSON string, from SoapUI to ensure I am testing with the same data.

Because the PUT is working with SoapUI the issue seems to be how I am trying to PUT the data.

I would appreciate it if someone could point me in the right direction with my Client configuration and the way I am trying to PUT the JSON body.

I have tried changing the 'json' => $json_body to 'body => $json_body and then setting the 'Content-type' to 'application/json' in the header but this made no difference to the result I am getting

via Chebli Mohamed