curl --request GET \
  --url https://api.hubapi.com/crm/v3/limits/associations/labels \
  --header 'Authorization: Bearer <token>'

{
  "results": [
    {
      "allLabels": [
        "<string>"
      ],
      "fromObjectType": {
        "objectTypeId": "<string>",
        "pluralLabel": "<string>",
        "singularLabel": "<string>"
      },
      "limit": 123,
      "percentage": 123,
      "toObjectType": {
        "objectTypeId": "<string>",
        "pluralLabel": "<string>",
        "singularLabel": "<string>"
      },
      "usage": 123
    }
  ]
}