const options = {
  method: 'PUT',
  headers: {'X-API-Key': '<api-key>', 'Content-Type': 'application/json'},
  body: JSON.stringify({records: [{priority: 1, weight: 1, port: 1, target: '<string>'}]})
};

fetch('https://api.mailchannels.net/inbound/v1/domains/{domain}/downstream-address', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

import requests

url = "https://api.mailchannels.net/inbound/v1/domains/{domain}/downstream-address"

payload = { "records": [
        {
            "priority": 1,
            "weight": 1,
            "port": 1,
            "target": "<string>"
        }
    ] }
headers = {
    "X-API-Key": "<api-key>",
    "Content-Type": "application/json"
}

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

print(response.text)

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.mailchannels.net/inbound/v1/domains/{domain}/downstream-address",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "PUT",
  CURLOPT_POSTFIELDS => json_encode([
    'records' => [
        [
                'priority' => 1,
                'weight' => 1,
                'port' => 1,
                'target' => '<string>'
        ]
    ]
  ]),
  CURLOPT_HTTPHEADER => [
    "Content-Type: application/json",
    "X-API-Key: <api-key>"
  ],
]);

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

curl_close($curl);

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

curl --request PUT \
  --url https://api.mailchannels.net/inbound/v1/domains/{domain}/downstream-address \
  --header 'Content-Type: application/json' \
  --header 'X-API-Key: <api-key>' \
  --data '
{
  "records": [
    {
      "priority": 1,
      "weight": 1,
      "port": 1,
      "target": "<string>"
    }
  ]
}
'

{
  "records": [
    {
      "priority": 1,
      "weight": 1,
      "port": 1,
      "target": "<string>"
    }
  ]
}

{
  "errors": [
    "<string>"
  ],
  "code": 123,
  "message": "<string>"
}

{
  "errors": [
    "<string>"
  ],
  "code": 123,
  "message": "<string>"
}

{
  "errors": [
    "<string>"
  ],
  "code": 123,
  "message": "<string>"
}

{
  "errors": [
    "<string>"
  ],
  "code": 123,
  "message": "<string>"
}