If you're working with WhatsApp data channel flow JSON and see this error:

INVALID_ROUTING_MODEL: Backward route [(destination)-)(source)] corresponding to forward route [(source)-)(destination)] is not allowed in the routing model. Only forward routes can be specified.

You're likely defining bidirectional routing, which the system doesn't support. Here’s why it happens and how to fix it.

What This Error Means

The routing model in WhatsApp flows must only move forward. You cannot define a path from Screen A to Screen B and then also from B back to A. That creates a backward route, which is not allowed.

Example That Triggers the Error

{
  "routing_model": {
    "FIRST_SCREEN": ["SECOND_SCREEN"],
    "SECOND_SCREEN": ["FIRST_SCREEN"]
  }
}

This setup tells the system:

  • FIRST_SCREEN leads to SECOND_SCREEN

  • But SECOND_SCREEN also leads back to FIRST_SCREEN

This two-way routing creates a loop that prevents a clear forward flow, resulting in the INVALID_ROUTING_MODEL error.

How to Fix It

To resolve the error:

  • Remove any reverse or backward links in your routing_model

  • Ensure that your flow only moves one-way from screen to screen

Fixed Example

{
  "routing_model": {
    "FIRST_SCREEN": ["SECOND_SCREEN"]
  }
}

In this version:

  • The flow moves from FIRST_SCREEN to SECOND_SCREEN

  • There is no route going back

  • This structure is valid and won’t trigger an error

If your experience requires users to “go back,” it should be implemented using a different mechanism—like restarting the flow, using a separate path, or offering a new interaction from a terminal screen.

For more troubleshooting insights related to WhatsApp Business API, check out heltar.com/blogs.