# Add to metadata set

Add an item to a metadata set.

A metadata set is an array of unique values. This endpoint ensures that the metadata at the given path is treated as a set:
- If the path is empty or does not exist, it is initialized as an empty array.
- If the value already exists in the set, it is not added again.
- The metadata at the path must be an array (or empty).

### Example
If current metadata is `{"tags": ["a"]}`, adding `"b"` to path `"tags"` results in `{"tags": ["a", "b"]}`.
Adding `"a"` again results in no change.

## Endpoint signature

```http
POST https://api.reservepay.com/merchants/add-to-metadata-set HTTP/1.1
Content-Type: application/json
Accept: application/json
Authorization: Bearer <token>

{
  key: string,
  path: string?,
  value: any,
  version: number?,
  ttl: number?,
}
```

Returns: boolean

## Request arguments

### `key` (string)

**Required**. The unique key for the metadata.

### `path` (string)

_Optional_. Optional dot-separated path within the metadata object.

### `value` (any)

**Required**. The value to add to the set.

### `version` (number)

_Optional_. The version number for optimistic locking.

### `ttl` (number)

_Optional_. The time to live in seconds. Affects the whole metadata object, not just the value at path.

## Errors common to all endpoints

### `UNHANDLED_ERROR`

This error occurs when the server encounters an unexpected internal error that
it cannot handle gracefully. This typically happens due to bugs, infrastructure
issues, or edge cases that weren't anticipated during development.

### `INVALID_ARGUMENTS`

This error occurs when the request contains invalid or missing parameters.
Common cases include missing required fields, or values that don't match the
expected format or type.

### `BAD_VERSION`

This error occurs when making requests to an API version that does not exist.
This commonly happens when using an outdated SDK or when the API version
specified in the request URL is incorrect.