curl --request POST \
  --url http://{host}:{port}/{contextPath}/process-instance/{id}/modification \
  --header 'Authorization: Basic <encoded-value>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "skipCustomListeners": true,
  "skipIoMappings": true,
  "instructions": [
    {
      "type": "startBeforeActivity",
      "activityId": "activityId",
      "variables": {
        "var": {
          "value": "aVariableValue",
          "local": false,
          "type": "String"
        },
        "varLocal": {
          "value": "anotherVariableValue",
          "local": true,
          "type": "String"
        }
      }
    },
    {
      "type": "cancel",
      "activityInstanceId": "anActivityInstanceId"
    }
  ],
  "annotation": "Modified to resolve an error."
}
'

import requests

url = "http://{host}:{port}/{contextPath}/process-instance/{id}/modification"

payload = {
    "skipCustomListeners": True,
    "skipIoMappings": True,
    "instructions": [
        {
            "type": "startBeforeActivity",
            "activityId": "activityId",
            "variables": {
                "var": {
                    "value": "aVariableValue",
                    "local": False,
                    "type": "String"
                },
                "varLocal": {
                    "value": "anotherVariableValue",
                    "local": True,
                    "type": "String"
                }
            }
        },
        {
            "type": "cancel",
            "activityInstanceId": "anActivityInstanceId"
        }
    ],
    "annotation": "Modified to resolve an error."
}
headers = {
    "Authorization": "Basic <encoded-value>",
    "Content-Type": "application/json"
}

response = requests.post(url, json=payload, headers=headers)

print(response.text)

const options = {
  method: 'POST',
  headers: {Authorization: 'Basic <encoded-value>', 'Content-Type': 'application/json'},
  body: JSON.stringify({
    skipCustomListeners: true,
    skipIoMappings: true,
    instructions: [
      {
        type: 'startBeforeActivity',
        activityId: 'activityId',
        variables: {
          var: {value: 'aVariableValue', local: false, type: 'String'},
          varLocal: {value: 'anotherVariableValue', local: true, type: 'String'}
        }
      },
      {type: 'cancel', activityInstanceId: 'anActivityInstanceId'}
    ],
    annotation: 'Modified to resolve an error.'
  })
};

fetch('http://{host}:{port}/{contextPath}/process-instance/{id}/modification', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_PORT => "62437",
  CURLOPT_URL => "http://{host}:{port}/{contextPath}/process-instance/{id}/modification",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "POST",
  CURLOPT_POSTFIELDS => json_encode([
    'skipCustomListeners' => true,
    'skipIoMappings' => true,
    'instructions' => [
        [
                'type' => 'startBeforeActivity',
                'activityId' => 'activityId',
                'variables' => [
                                'var' => [
                                                                'value' => 'aVariableValue',
                                                                'local' => false,
                                                                'type' => 'String'
                                ],
                                'varLocal' => [
                                                                'value' => 'anotherVariableValue',
                                                                'local' => true,
                                                                'type' => 'String'
                                ]
                ]
        ],
        [
                'type' => 'cancel',
                'activityInstanceId' => 'anActivityInstanceId'
        ]
    ],
    'annotation' => 'Modified to resolve an error.'
  ]),
  CURLOPT_HTTPHEADER => [
    "Authorization: Basic <encoded-value>",
    "Content-Type: application/json"
  ],
]);

$response = curl_exec($curl);
$err = curl_error($curl);

curl_close($curl);

if ($err) {
  echo "cURL Error #:" . $err;
} else {
  echo $response;
}

package main

import (
	"fmt"
	"strings"
	"net/http"
	"io"
)

func main() {

	url := "http://{host}:{port}/{contextPath}/process-instance/{id}/modification"

	payload := strings.NewReader("{\n  \"skipCustomListeners\": true,\n  \"skipIoMappings\": true,\n  \"instructions\": [\n    {\n      \"type\": \"startBeforeActivity\",\n      \"activityId\": \"activityId\",\n      \"variables\": {\n        \"var\": {\n          \"value\": \"aVariableValue\",\n          \"local\": false,\n          \"type\": \"String\"\n        },\n        \"varLocal\": {\n          \"value\": \"anotherVariableValue\",\n          \"local\": true,\n          \"type\": \"String\"\n        }\n      }\n    },\n    {\n      \"type\": \"cancel\",\n      \"activityInstanceId\": \"anActivityInstanceId\"\n    }\n  ],\n  \"annotation\": \"Modified to resolve an error.\"\n}")

	req, _ := http.NewRequest("POST", url, payload)

	req.Header.Add("Authorization", "Basic <encoded-value>")
	req.Header.Add("Content-Type", "application/json")

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(string(body))

}

HttpResponse<String> response = Unirest.post("http://{host}:{port}/{contextPath}/process-instance/{id}/modification")
  .header("Authorization", "Basic <encoded-value>")
  .header("Content-Type", "application/json")
  .body("{\n  \"skipCustomListeners\": true,\n  \"skipIoMappings\": true,\n  \"instructions\": [\n    {\n      \"type\": \"startBeforeActivity\",\n      \"activityId\": \"activityId\",\n      \"variables\": {\n        \"var\": {\n          \"value\": \"aVariableValue\",\n          \"local\": false,\n          \"type\": \"String\"\n        },\n        \"varLocal\": {\n          \"value\": \"anotherVariableValue\",\n          \"local\": true,\n          \"type\": \"String\"\n        }\n      }\n    },\n    {\n      \"type\": \"cancel\",\n      \"activityInstanceId\": \"anActivityInstanceId\"\n    }\n  ],\n  \"annotation\": \"Modified to resolve an error.\"\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("http://{host}:{port}/{contextPath}/process-instance/{id}/modification")

http = Net::HTTP.new(url.host, url.port)

request = Net::HTTP::Post.new(url)
request["Authorization"] = 'Basic <encoded-value>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"skipCustomListeners\": true,\n  \"skipIoMappings\": true,\n  \"instructions\": [\n    {\n      \"type\": \"startBeforeActivity\",\n      \"activityId\": \"activityId\",\n      \"variables\": {\n        \"var\": {\n          \"value\": \"aVariableValue\",\n          \"local\": false,\n          \"type\": \"String\"\n        },\n        \"varLocal\": {\n          \"value\": \"anotherVariableValue\",\n          \"local\": true,\n          \"type\": \"String\"\n        }\n      }\n    },\n    {\n      \"type\": \"cancel\",\n      \"activityInstanceId\": \"anActivityInstanceId\"\n    }\n  ],\n  \"annotation\": \"Modified to resolve an error.\"\n}"

response = http.request(request)
puts response.read_body

{
  "type": "<string>",
  "message": "<string>",
  "code": 123
}

{
  "type": "<string>",
  "message": "<string>",
  "code": 123
}