Messages in Sendo have an optional metadata field, which you can use to store additional, structured information about the message. This can be useful for tracking information about the message, such as the user’s unique identifier from your system.

Metadata must be a set of key-value pairs (strings), which you can include as metadata in the request body when sending a message. The metadata will be returned when you retrieve the message, and sent with any associated webhook events.

You can specify up to 50 keys, with key names up to 40 characters long and values up to 500 characters long. The API request will error if the metadata is invalid.