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

{
  "totalRecordsAtLimit": 123,
  "atLimitFromRecordSamples": [
    {
      "label": "<string>",
      "objectId": 123
    }
  ],
  "totalRecordsNearLimit": 123,
  "limit": 123,
  "nearLimitFromRecordSamples": [
    {
      "usage": 123,
      "percentage": 123,
      "label": "<string>",
      "objectId": 123
    }
  ]
}