RCS isn't always deliverable — a recipient's device or carrier might not support it, your Agent might not have launched there yet, or the message might expire before it gets through. When that happens, Naxai can automatically send an SMS instead, using your Sender Service's own phone numbers.

When fallback happens

Fallback is triggered when:

• The recipient's device isn't RCS-capable, or their carrier doesn't support RCS
• Your Agent hasn't launched on the recipient's carrier
• The message expires before it can be delivered as RCS

See RCS Status & Error Codes for the exact codes you'll see when this happens (600-fallback-sms-incompatible, 601-fallback-sms-expired, 602-fallback-sms-generic).

How fallback works

Fallback re-uses the same Sender Service model as SMS: the phone numbers in your Sender Service's pool are what send the fallback SMS. See Sender Services if you need to add numbers to yours.

To enable fallback, provide:

• senderServiceId — the Sender Service whose numbers will send the fallback SMS
• body — the SMS text to send, up to 4096 characters, with Liquid personalization supported
• type — SMS encoding: auto, text, or unicode (default text)

You configure this wherever you send RCS:

• Sending via the API: include a fallback object in your request, see Sending RCS Messages via API
• Sending via RCS Broadcasts: add fallback text when composing your broadcast

What's next

• RCS Status & Error Codes
• Sending RCS Messages via API
• RCS Broadcasts