uid from reeview_uid — see Shoppable videos order tracking. Live shopping sends lsId from reeview_lsid — see Live shopping order tracking.
Install the pixel once per storefront. That one install covers widgets and live shows.
Install the pixel for your platform:
Shopify
Custom pixel in Settings → Customer events.
Magento
Included on the default thank-you page; optional extra placements.
Salesforce Commerce Cloud
Included on the default order confirmation page; optional extra placements.
Other / GTM
Custom snippet or Google Tag Manager.
trackingPixel after checkout instead of installing a web pixel.