GetExternalContactAction returning 400 on phone lookup

Trying to wire up a custom lookup via GetExternalContactAction. The goal is simple: pass the caller’s phone number to our endpoint and get back the customer ID.

The endpoint works fine in Postman. I’m passing the phone as a query param like ?phone=+525512345678. Returns 200 with the JSON payload.

Inside Architect, I’ve got the action configured. Method is GET. URL is set. The issue is the request mapping. I tried mapping the {{contact.phone}} variable directly to the query parameter. The action fails with a 400 Bad Request from our server. The logs show the phone number is coming through as an empty string.

Here’s the mapping JSON I’m using in the data action:

{
 "method": "GET",
 "url": "https://api.example.com/lookup",
 "queryParams": {
 "phone": "{{contact.phone}}"
 }
}

Is contact.phone the right variable? I’ve also tried {{interaction.contact.phone}} but that just breaks the JSON parsing in Architect. The variable definitely has a value because I can see it in the flow logs right before the action.

Any idea why the mapping is stripping the value?