4009: Sender line has no RCS account

The sender line has no RCS account configured, so its RCS capability cannot be determined. This is an HTTP 503 error about the sender line on your account, not the recipient — retrying will not help until the line is repaired.

Do not treat this as “the recipient does not support RCS”. The check produced no answer about the recipient at all.

• Send from a different line on your account, or send without preferred_service so delivery falls back to SMS.
• Contact support to have RCS re-enabled on the affected line.