63016: Outside messaging window. For WhatsApp, use a Message Template instead

This error occurs when you send a free-form message after the channel's allowed session window has closed. For WhatsApp, business-initiated messages sent outside the 24-hour customer service window must use an approved template. Send that template with ContentSid and, if needed, ContentVariables. Since April 1, 2025, sending a WhatsApp template in Body outside the customer service window fails with this error.

• You sent a free-form WhatsApp message more than 24 hours after the user's last inbound message.
• You tried to send a WhatsApp template outside the customer service window using Body instead of ContentSid and ContentVariables.
• You used a content type that cannot start a business-initiated WhatsApp conversation, such as twilio/list-picker or twilio/location.
• You tried to send a Facebook Messenger message outside its user-initiated 24-hour response window.

• Wait for the user to send a new inbound message if you need to continue a free-form WhatsApp conversation.
• If you need to message the user outside the 24-hour window, create or use an approved WhatsApp template and send it with ContentSid.
• Remove Body and MediaUrl when you send a content template. Pass placeholder values in ContentVariables.
• Use a content type supported for business-initiated WhatsApp messages. Do not use twilio/list-picker or twilio/location for out-of-session sends.
• For Facebook Messenger, only respond after the user has messaged your page and send your reply within the 24-hour window.

• Send WhatsApp notification messages with templates
• Send templates created with the Content Template Builder
• Session Definitions