get https://preview.vouchery.io/api/v1.0/vouchers/find
Find voucher by campaign metadata.
Optionally assign found voucher to a customer by passing customer_identifier param. All vouchers for a customer can be fetched at /customers/{id}/vouchers.
If no voucher is available this endpoint will return an empty response and HTTP code 204 No content
At least one metadata must be provided, otherwise no voucher will be returned.