1. Google Tag Manager must be installed on your site as described in the Google Tag Documentation: https://developers.google.com/tag-platform/tag-manager/web

2. Event tracking must be set up. See our guide for more information: https://tonic.uservoice.com/knowledgebase/articles/2005207-google-tag-manager

You must allow your Google Tag to run on our designmynight.com domain from your Analytics admin.

Please refer to Google's guide on this: Set up cross-domain measurement via the Admin | Google Analytics Help

Your domains should look similar to our example below:

Once your domains are set up Cross Domain tracking should be working.

You can verify that the URL for the Tonic Checkout contains the linker parameter _gl; for example: https://tickets.designmynight.com/checkout?_gl=1*abcde5*.