curl --request POST \
  --url https://api.hubapi.com/crm/associations/v4/{fromObjectType}/{toObjectType}/labels \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "label": "<string>",
  "name": "<string>",
  "inverseLabel": "<string>"
}
'

{
  "results": [
    {
      "typeId": 123,
      "label": "<string>"
    }
  ]
}