Input to create the transaction.

Choose one of the available messages.

If the transaction is designated to be signed by a specific signer, this field should be set.

Format: users/{email} or users/{id}

Example: ["users/[email protected]"] or ["users/a3e4f5"]

Arbitrary client-defined key/value metadata to attach to the transaction.

Utila stores these values but never interprets them. They are surfaced
read-only on the resulting Transaction to anyone who can view it (custodians,
partners, integrations), so multiple integrations can namespace their own
keys without colliding.

This field is meant for small, lightweight metadata rather than bulk data:

• At most 64 entries.
• Keys: at most 256 characters.
• Total serialized size (UTF-8): at most 64 KiB (65,536 bytes).

Avoid storing secrets or sensitive data here, since the data is visible to
other parties who can view the transaction. For anything larger than the
size limit, consider keeping it in your own system and referencing it by an ID.