curl --request POST \
  --url https://sandbox.api.app.firstsales.io/api/v1/organizations/{orgId}/workspaces/{wsId}/contacts/merge \
  --header 'Authorization: Bearer <token>'

const options = {method: 'POST', headers: {Authorization: 'Bearer <token>'}};

fetch('https://sandbox.api.app.firstsales.io/api/v1/organizations/{orgId}/workspaces/{wsId}/contacts/merge', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

{}

{
  "error": {
    "code": "<string>",
    "message": "<string>",
    "requestId": "<string>",
    "details": {}
  }
}