curl --request PUT \
  --url https://api.hubapi.com/crm/associations/2026-03/{fromObjectType}/{toObjectType}/labels \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "associationTypeId": 123,
  "label": "<string>",
  "inverseLabel": "<string>"
}
'

This response has no body data.