Wix

Tag Installation

Wix now allows GTM to be installed.
https://support.wix.com/en/article/adding-your-google-tag-manager-account-id-to-your-wix-site

1. Go to your site's Marketing Integrations tab.
2. Go to Google Tag Manager and click Go For It.
3. At the top right click Connect Google Tag Manager.
4. Enter your Google Tag Manager container ID.
5. Click Save.

Form Tracking

The contact form in Wix will use the event "lead"

Sale Tracking

The tracking should be set up automatically when the Tag Manager Integration is setup.
The events / variables are:

purchase
ecommerce.purchase.actionField.revenue
ecommerce.purchase.actionField.transactionId