ExternalMetadata is a string-string key-value store that can be used to store information known at the time of resource creation. This way it can be retrieved later on, for instance when a payment or expected transaction is reconciled with the booked transaction on the bank statement. ExternalMetadata can have at most 20 entries. Keys may have a maximum length of 64 chars and values a maximum length of 512 chars. By default, this field is optional. It is possible to make it required in the Atlar Dashboard by visiting the Metadata keys page. Requirement rules can be specified per API resource. Both the Dashboard and the API will then enforce these rules and give validation errors when the required fields are not set.