API · Contact properties

Create Contact Property

Create a string or number property for contacts (requires full access). Your team can have up to 100 properties, and property keys keep their original spelling.

POST/contact-propertiesFull access

Request parameters

Parameter	Type	Description
`Idempotency-Key` header · optional	`string` 1–256 characters	Makes the request safe to retry. See Idempotency.
`key` body · required	`string` Matches /^[a-zA-Z0-9_]{1,50}$/	Case-preserved key of 1–50 letters, numbers, or underscores, excluding email, first_name, last_name, and unsubscribed.
`type` body · required	`"string" \| "number"`	Property value type: string or number.
`fallback_value` body · optional	`string \| number`	Default matching the property type, with strings up to 1000 characters preserved exactly, including whitespace and empty strings; null is rejected.

Request example

Set OPENSEND_BASE_URL=https://api.example.com and OPENSEND_API_KEY=os_replace_me on your server.

bash

curl -X POST "$OPENSEND_BASE_URL/contact-properties" \
  -H "Authorization: Bearer $OPENSEND_API_KEY" \
  -H 'Content-Type: application/json' \
  -d '{"key":"plan","type":"string","fallback_value":"starter"}'

Response

201 · application/json. Example IDs stand for IDs returned by your installation.

json

{
  "object": "contact_property",
  "id": "YOUR_ID"
}

Behavior and errors

At most 100 properties per team. Boolean values are unsupported. Deletion hides the property immediately and removes contact values in batches; the key stays reserved until cleanup finishes.

Use a full-access credential. Resource IDs belong to your team; an unknown or foreign resource returns 404. See authentication, errors, rate limits, and compatibility for the shared contract.