curl --request POST \
  --url https://api.salessequencer.com/api/v1/campaigns/{campaign_id}/mailboxes/add \
  --header 'Content-Type: application/json' \
  --header 'X-API-Key: <api-key>' \
  --data '
{
  "mailbox_ids": [
    123
  ]
}
'

import requests

url = "https://api.salessequencer.com/api/v1/campaigns/{campaign_id}/mailboxes/add"

payload = { "mailbox_ids": [123] }
headers = {
    "X-API-Key": "<api-key>",
    "Content-Type": "application/json"
}

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

print(response.text)

const options = {
  method: 'POST',
  headers: {'X-API-Key': '<api-key>', 'Content-Type': 'application/json'},
  body: JSON.stringify({mailbox_ids: [123]})
};

fetch('https://api.salessequencer.com/api/v1/campaigns/{campaign_id}/mailboxes/add', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));