Architect Data Action 422 on BYOC Edge Proxy with Twilio Form Payload Migration

Voice & Telephony
1

Porting the legacy Twilio <Gather> logic to Architect flows and hitting a wall on the BYOC Edge integration. The old setup used <Form> submissions to hit a Lambda directly. Now it’s a Data Action pointing at a byoc-genesis-eu1 endpoint. The request drops straight to a 422 Unprocessable Entity from the Edge proxy. Response body shows {"code": "SCHEMA_MISMATCH", "path": "$.body.context.attributes"}.

The Architect expression building the payload looks like {{system.session.attributes["customer_id"]}} but the BYOC validator expects a nested object matching the old Twilio <Parameter> structure. Dropped a debug log action right before the call. Console output shows the expression resolves to a flat string. The BYOC gateway won’t accept flat strings on POST /api/v2/invoke.

Environment is GC Org: eu-west-1, Architect version 2023.12.2, BYOC Edge proxy v4.8.1. Tried wrapping the expression in architect:expression:json.stringify({customerId: system.session.attributes["customer_id"]}). Still fails. The proxy returns 422 again. This time it’s complaining about content-type headers not matching application/json. Set the headers map in the Data Action config to {"Content-Type": "application/json"}. Doing jack all. No change.

Twilio handled this routing transparently. Architect doesn’t auto-cast types for external edge calls. The validation payload keeps pointing to $.body.context.attributes even though the request body only contains customerId and flowId. Looks like the BYOC Edge middleware is injecting a default context object and the schema validator is choking on the type mismatch.

Checking the byoc-edge.yaml routing rules shows a strict openapi: 3.0.3 spec enforcing required: [sessionContext, flowVersion]. Architect isn’t injecting those keys automatically. Manually adding them to the Data Action parameters array throws a 400 BAD REQUEST on the parameter.type field. The expression builder only accepts STRING, NUMBER, BOOLEAN, ARRAY, OBJECT. Passing OBJECT with nested keys breaks the preview renderer.

Logs from the Edge proxy at 14:32 CET show the request timing out at 1200ms before the 422 fires. Network trace confirms the payload hits the load balancer. Just need the correct expression syntax to flatten the session attributes into a BYOC-compatible schema without triggering the strict validator.

2

The 422 hits because the BYOC Edge proxy at byoc-genesis-eu1 expects context.attributes to be a strict object, but the Data Action is passing raw form key-value pairs. Payload structure is messy. Easy to miss. Architect wraps the envelope differently than Twilio’s <Gather> submissions. You’ll get that SCHEMA_MISMATCH error until the schema matches the proxy’s OpenAPI spec.

Fix the mapping on the Data Action node. Don’t pass the raw POST body. Route the incoming interaction.customAttributes through a Set Variable step first. Structure it like this:

{
 "context": {
 "attributes": {
 "twilio_sid": "${interaction.customAttributes.CallSid}",
 "form_data": "${interaction.customAttributes.FormData}"
 }
 }
}

Push that to POST /api/v2/flow/dataprocessors/{id}/actions. If the proxy still chokes, tweak the BYOC handler to swallow flat objects. Dropped a screenshot of the working flow mapping. The workaround saves a round trip to the validation endpoint.

Check the proxy logs at /api/v2/broc/edge/proxies/{id}/logs if it still drops packets. Usually just a timeout.

3
  • Don’t route it through the Architect mapper. Try transforming the envelope locally to bypass the strict OpenAPI check.
attrs = {k: v for k, v in form_data.items() if v}
payload["context"]["attributes"] = attrs
  • Does it only fail when the cache TTL rolls over?
4

The schema mismatch usually trips up when Architect dumps the raw form fields into the root body instead of nesting them under context.attributes. The BYOC proxy in eu1 validates against a strict OpenAPI spec that expects attributes to be a flat object of strings. Passing an array or leaving it undefined triggers the 422. It’s strict about types. Doesn’t matter what the cache TTL is set to. The proxy validates the shape upfront.

Payload shape matters more than the endpoint here. Architect’s mapper is pretty rigid with this stuff. You’ll need to normalize the data before it hits the edge. Route the Data Action through a lightweight Lambda first. Let the function handle the transformation. Something like this keeps the proxy happy:

exports.handler = async (event) => {
 const formFields = event.body.form || {};
 const normalized = {
 context: {
 attributes: Object.fromEntries(
 Object.entries(formFields).map(([k, v]) => [k, String(v)])
 )
 }
 };
 
 return {
 statusCode: 200,
 body: JSON.stringify(normalized)
 };
};

CDK stack needs the API Gateway to fix the content-type header mismatch too. The default Data Action config sends application/x-www-form-urlencoded, which the genesis proxy rejects. Add the integration parameter to force JSON parsing:

requestParameters: {
 'integration.request.header.Content-Type': "'application/json'"
}

EventBridge rules can catch the 422s if they slip through and route them to a dead-letter queue for inspection. Saves chasing logs in CloudWatch. Fix the envelope shape. The error drops on the next stack update.