Limitations

The following limitations must be considered when using metadata:

The number of metadata properties, that is, the length of the metadata array, cannot exceed 32 per entity.
Binary or binary-to-text encoded values, such as Base64, are not allowed. You should always provide external references should this type of data need to be associated with an entity.
Array nesting is not permitted, therefore a metadata entry of type array cannot contain another array inside of it.
The object type must always include a value that is JSON-serializable, as with all other objects in the API.
The length of the value field, when stringified, cannot exceed 1,024 characters. If this is a problem, you should consider breaking up the data into separate metadata entries.