curl --request POST \
  --url https://api.hubapi.com/integrations/v1/{application-id}/timeline/event-types/{event-type-id}/properties

[
  {
    "name": "NumericProperty",
    "label": "Numeric Property",
    "propertyType": "Numeric"
  },
  {
    "name": "company",
    "propertyType": "String",
    "label": "Company Name",
    "objectProperty": "company"
  },
  {
    "name": "size",
    "propertyType": "Enumeration",
    "label": "size",
    "options": [
      {
        "value": "large",
        "label": "Large"
      },
      {
        "value": "medium",
        "label": "Medium"
      },
      {
        "value": "small",
        "label": "Small"
      }
    ]
  }
]