Resend API (unofficial showcase)
POST/contact-properties

Create a contact property

Creates a custom property that you can use to store contact data. Supply key and type; use fallback_value to provide a default that matches the selected type.

  • IdempotentThe SDK sends Idempotency-Key, so a retried request is only applied once.

3 body fields

Contact property definition. Include the required key and type; fallback_value is optional.

keystringrequired
The property key. Max length is 50 characters. Only alphanumeric characters and underscores are allowed.
typestringrequired
The property type.
Allowed:stringnumber
fallback_valuestringoptional
The default value to use when the property is not set for a contact. Must match the type specified in the type field.

1 status code
201Returns the created contact property’s ID and the response object type.
idstringoptional
The ID of the contact property.
objectstringoptional
The object type of the response.

Error handling

key and type are required; key must be no more than 50 characters and contain only alphanumeric characters or underscores. type must be string or number, and fallback_value must match the selected type.