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Integrating Mida with CallRail: A Step-by-Step Guide

Attribute offline phone-call conversions to your Mida experiments with CallRail Custom Cookie Capture and a single webhook URL.

Overview

Integrating Mida with CallRail lets you close the loop on offline (phone-call) conversions. Mida already stores each visitor's ID in a first-party cookie named optimize_uuid. You tell CallRail to capture that cookie, then point a CallRail webhook at Mida's dedicated CallRail endpoint. When a call comes in, Mida reads the visitor's ID from the call payload, records a Phone Call event, and attributes it to the experiment the caller was in.

No code and no Zapier. Mida's CallRail endpoint accepts CallRail's native webhook payload as-is — there is no field mapping or custom body to build. Setup is two steps: capture one cookie, paste one URL. And because Mida matches event-based goals to experiments at report time, you can start capturing calls right away and create (or rename) the matching goal later — past calls from visitors who were in the test are credited retroactively.

💡 How the data flows

  1. The Mida tag sets the optimize_uuid cookie on your visitor.

  2. CallRail's Custom Cookie Capture stores that cookie with the visitor.

  3. The visitor calls your CallRail number.

  4. CallRail posts the call (including custom.optimize_uuid) to Mida's CallRail endpoint.

  5. Mida records a Phone Call event on that visitor.

  6. Your matching event goal credits the call to the caller's experiment.

Prerequisites

  • The Mida tracking code installed on your site (it sets the optimize_uuid cookie — nothing to add).

  • CallRail visitor tracking through a Website (Session) tracker number pool. This is required: CallRail does not attach captured cookies to calls placed to static source tracker numbers.

  • Permission in CallRail to configure Custom Cookie Capture and Webhooks.

  • Your Mida widget key (used as project_key in the webhook URL).

Step 1 — Capture the optimize_uuid cookie in CallRail

  1. In CallRail, open Integrations and select Custom Cookie Capture.

  2. Choose the company where you want to track visitors.

  3. Add optimize_uuid to the list of cookie names to capture, then Save.

CallRail Custom Cookie Capture integration with optimize_uuid in the Cookie Names field

From now on, when a tracked visitor calls one of your CallRail numbers, CallRail includes the cookie in the call webhook under a custom object — this is how Mida identifies the visitor:

{
  "custom": { "optimize_uuid": "a1b2c3d4e5" }
}

Step 2 — Point a CallRail webhook at Mida

  1. In CallRail, go to Integrations → Webhooks.

  2. Add a webhook on the Post-Call (Call Completed) trigger.

  3. Set the webhook URL to your account's regional Mida endpoint, replacing YOUR_KEY with your Mida widget key:

US region:  https://api-us.mida.so/abtest/callrail/webhook?project_key=YOUR_KEY
EU region:  https://api-eu.mida.so/abtest/callrail/webhook?project_key=YOUR_KEY

CallRail Webhooks integration with the Mida endpoint URL in the Post-Call field

Use the host that matches your Mida region. Mida is region-hosted, and a widget key only resolves on its own region's host, so an EU account must use api-eu and a US account must use api-us. If you are unsure of your region, check the API host in your Mida install snippet, or copy the exact URL shown in your Mida dashboard under Integrations → CallRail.

That is the entire configuration — CallRail only lets you set the destination URL, and Mida's endpoint is built for exactly that. CallRail posts its full call object, for example:

{
  "resource_id": "CAL8154748ez...",
  "answered": true,
  "duration": 43,
  "source": "Google Organic",
  "custom": { "optimize_uuid": "a1b2c3d4e5" }
}

Mida reads custom.optimize_uuid to find the visitor, records a Phone Call event, and stores useful call metadata (duration, answered, direction, source, and phone numbers) on the event. It also de-duplicates on the CallRail call id, so enabling both Post-Call and Call-Modified triggers will not double count. To record under a different event name, append &event_name=Your%20Event to the URL.

Optional — test it with cURL:

# use your account's regional host (api-us or api-eu)
curl -X POST "https://api-us.mida.so/abtest/callrail/webhook?project_key=YOUR_KEY" \
     -H "Content-Type: application/json" \
     -d '{"resource_id":"CAL123","answered":true,"duration":43,"custom":{"optimize_uuid":"a1b2c3d4e5"}}'

A successful call returns 200 "Event recorded successfully".

Step 3 — Create the Phone Call goal in Mida

In Mida, create a custom event goal whose event name matches the endpoint's event name (Phone Call by default), then attach it to the experiment(s) you want to measure as the primary metric or a secondary metric. Because event goals are matched at report time, every past call from a visitor who was in the test is credited automatically the next time you open the results — so you can start capturing calls first and decide how to attribute them later.

You can also start from your Mida dashboard under Integrations → CallRail → Enable, which links to this guide.

Troubleshooting & notes

  • Website (Session) pool is required. If a call was placed to a static source tracker number, CallRail sends no captured cookie and the endpoint returns an actionable 400 explaining the two prerequisites (cookie name optimize_uuid listed in Custom Cookie Capture, and a Website/Session tracker pool).

  • Retroactive, with one boundary. A call counts only for a caller who was assigned to the test when they visited and whose call falls within the test's active window. Defining the goal later is fine; being in the test is required.

  • Cookie must exist at call time. Custom Cookie Capture stores the cookie value present when CallRail tracks the visitor, so the Mida tag must have loaded during their visit.

  • No API key needed. The project_key in the URL authorizes the request.

  • Alternative (immediate) path. If you prefer to write the conversion the instant a call lands and already have a goal set up, you can instead POST to your regional host (https://api-us.mida.so or https://api-eu.mida.so) at /abtest/webhook with a goal key plus mida_uuid. It records immediately but requires the goal to exist first and will not back-fill past calls.

Conclusion

Capture Mida's optimize_uuid cookie in CallRail and paste one webhook URL — that is all it takes to bring offline phone conversions into your experiments, with no code, no Zapier, and no field mapping to maintain. Attach the Phone Call goal as a primary or secondary metric and Mida retroactively credits every call from visitors who were in your tests.

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