Create a contact property
POST/v1/contact-properties
A custom field you can store on contacts and use in broadcasts as {{{key}}}. The fallback is used when a contact has no value.
Required scope: contacts:manage
Request body
| Field | Type |
|---|---|
keyrequired | string |
typerequired | "string" | "number" |
fallback_valueoptional | any |
Unknown fields are rejected, so a typo never silently does nothing.
Example
curl -X POST 'https://api.sendsend.email/v1/contact-properties' \
-H "Authorization: Bearer $SENDSEND_API_KEY" \
-H 'Content-Type: application/json' \
-d '{
"key": "plan",
"type": "string",
"fallback_value": "free"
}'Response 201
{
"id": "prop_Lm4…",
"object": "contact_property",
"key": "plan",
"type": "string",
"fallback_value": "free",
"created_at": "2026-10-06T15:00:00.000Z"
}Errors
| Status | Code | When |
|---|---|---|
| 400 | validation_error | The request body or parameters are invalid. The message says which field. |
| 409 | validation_error | A property with that key exists. |
| 401 | unauthorized | The API key is missing, invalid or revoked. |
| 403 | forbidden | The key does not have the scope this endpoint needs. |
Every error has the same shape. See Errors.