There are two steps to correctly install Tend on Shopify:
Go to the theme editor at https://myshopify.com/admin/themes. Then select the Edit HTML/CSS option.
Within the theme.liquid file (this file may be different depending on your theme), copy/paste the Tracking Code from your Tend account, just above the
Within Shopify, go to Settings > Checkout. There, scroll down to "Additional Scripts." Here, place the Tracking Code from your Tend Account, along with the TendID script for shopify. Should end up with something like...
Since Shopify does not allow you to install a script on the checkout pages, TendID is used to "push" the customer's email into Tend.
And that's it! Of course, let us know if we can help!