Start process from rest api - php

I have referred this link for understand about rest api. It confuse me, I don’t know how to complete it from php code. I have tried as per above link in curl command but I get 405 method not allowed error

my start process contains the form too, I think I need to pass form values as json but I don’t know where should I declare and where should I pass. Most of the document they mention pass the json header but all incomplete.

can anyone share snippet to reproduce of start camunda process from php rest api?

full code snippet for start process from php using rest api

    $data = array(
                    "variables"=> array(
                    "order_id"=> array("value"=>"12345","type"=>"String"),
    $data_string = json_encode($data);

    $ch = curl_init('');
    curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
    curl_setopt($ch, CURLOPT_POSTFIELDS, $data_string);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_HTTPHEADER, array(
            'Content-Type: application/json',
            'Content-Length: ' . strlen($data_string))

    $result = curl_exec($ch);