Question

What does the You are sending both client-side and server-side data to this destination warning mean in the Delivery Overview for destinations, and will it cause duplicate events for downstream destinations?

Product

Twilio Segment

Environment

Segment Console

Answer

This warning appears in the Delivery Overview because a particular destination supports both device-mode (client-side) and cloud-mode (server-side) connections simultaneously.

For setups like mobile sources to Braze Classic, events are sent in cloud-mode by default. However, if you manually bundle the Segment-Braze SDK into your mobile app, it will route the events to Braze in device-mode. Segment’s deduplication logic ensures that events are not sent twice.

In your Delivery Overview UI, you should expect to see the MESSAGE_SENT_CLIENT_SIDE error for these events. This indicates that the event has already been successfully sent via the client side. To prevent duplication, Segment intentionally prevents the cloud-mode event from sending and marks it as "Filtered at destination".

Additional Information 

For the most accurate setup guidance, refer to Segment’s official documentation for your specific destination.