Send a fax document to a specified number using the configured fax provider.
Recipient fax number (E.164 format preferred)
Sender fax number (optional, uses default if not provided)
Subject line for the fax
Optional provider override (uses default if not specified)
Default Response
Unique fax identifier
Current fax status
Provider used to send the fax
Recipient fax number
Sender fax number
ISO timestamp when fax was created
Estimated delivery time (ISO timestamp)