curl --request POST \
  --url https://api.qa.sima.ag/app_dev.php/api/v2/third_party/assignments/from_establishment \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: */*' \
  --header 'X-SIMA-SYSTEM-ID: <api-key>' \
  --data '
"\"{\\n    \\\"establishment_id\\\": 32,\\n    \\\"user_id\\\": 17\\n}\""
'

import requests

url = "https://api.qa.sima.ag/app_dev.php/api/v2/third_party/assignments/from_establishment"

payload = "\"{\n    \\"establishment_id\\": 32,\n    \\"user_id\\": 17\n}\""
headers = {
    "Authorization": "Bearer <token>",
    "X-SIMA-SYSTEM-ID": "<api-key>",
    "Content-Type": "*/*"
}

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

print(response.text)

const options = {
  method: 'POST',
  headers: {
    Authorization: 'Bearer <token>',
    'X-SIMA-SYSTEM-ID': '<api-key>',
    'Content-Type': '*/*'
  },
  body: JSON.stringify('"{\n    \"establishment_id\": 32,\n    \"user_id\": 17\n}"')
};

fetch('https://api.qa.sima.ag/app_dev.php/api/v2/third_party/assignments/from_establishment', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.qa.sima.ag/app_dev.php/api/v2/third_party/assignments/from_establishment",
  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('"{\\n    \\"establishment_id\\": 32,\\n    \\"user_id\\": 17\\n}"'),
  CURLOPT_HTTPHEADER => [
    "Authorization: Bearer <token>",
    "Content-Type: */*",
    "X-SIMA-SYSTEM-ID: <api-key>"
  ],
]);

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

curl_close($curl);

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

{
  "newAssignmets": 1,
  "newPlotDefaultCreated": true
}