Laravel HTTP Client multiple times the same key for JSON Post-Data

I want to send a JSON post to an API using the Laravel HTTP function. This is working great so far.

The API is Paperless NGX and its documentation stipulates that if you want to transfer a new document to Paperless via API, you can “tag” it directly. If I just define one day everything works. If you have multiple tags, you should use the “tags” key multiple times. So for each day a POST field “tags” is given and an ID is specified for each.

Paperless REST API Document Upload Documentation

But Laravel always only sends the last “tags” field.

How can I change this?

$response = Http::withHeaders( [ 'Authorization' => 'Token XXXXXXX'])
            ->attach( 'document', Storage::get($filename_storage), $filename, ['Content-Type' => 'application/pdf'] )
            ->post('https://xxxxxxxxxxxxxx/api/documents/post_document/' , [
                'tags' => '123',
                            'tags' => '456'
            ]);

Unfortunately I can’t get any further.