sendSms sends one SMS and can ask Brevo to call a message-specific delivery
webhook.
Example
Inputs
Output
Returns{ messageId: string }; numeric provider IDs are normalized to strings.
SMS credits are consumed per segment, not merely per action call. Long content,
the organization prefix, and Unicode encoding can split a message into multiple
segments and consume multiple credits. Sender rules, marketing restrictions,
and delivery availability vary by destination country.