The following resources:

can hold metadata on creation or be updated with new or changed metadata. Metadata is stored as a flat JSON object, with arrays, strings, numbers or null being valid value types. Storing metadata is recommended for associating information in your own system with resources in payments.

An example of a valid metadata JSON is

  // Other request parameters
  "metadata": {
    "customer_id": 12345,
    "shipping_details": "Customer wants it now"