curl --request POST \
  --url https://api.hubapi.com/crm/v3/properties/{objectType}/groups \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "displayOrder": -1,
  "label": "My Property Group",
  "name": "mypropertygroup"
}
'

{
  "displayOrder": -1,
  "label": "My Property Group",
  "name": "mypropertygroup"
}