Every ecommerce Plugin includes functionality for sending out transactional emails for things like purchase receipts, password resets, admin notifications, product expirations, and so on.
MemberPress (MP), Easy Digital Downloads (EDD), Restrict Content Pro (RCP), and Digital Access Pass (DAP) all include email functionality—including an editor—where you can determine the content of emails that will be sent to your customers.
(WooCommerce also does transactional email, but in somewhat mystifying fashion, it doesn’t give you an easy way to edit those emails. Very disappointing! Regardless, Woo sucks otherwise and will slow your site down to an unacceptable degree, so I never recommend using it.)
Anyway, the good ecommerce Plugins mentioned above do include email editors that operate much like the WordPress Classic Editor (specifically, with Visual and Text views).
And as it turns out, you can paste GRT for Email output into the Text tab of these editors to add beautifully formatted transactional emails to your ecommerce store 🏆
Check out these purchase receipt examples from Easy Digital Downloads, which I use to run DIYthemes:
Before:

A sad, unformatted purchase receipt from EDD 😔
After:

A much happier, GRT-formatted purchase receipt from EDD 🤩
And your emails can be way more sophisticated, too. Here’s the new purchase receipt for the Focus WordPress Theme; notice how I used horizontal rules to break up the email into digestible sections:

Holy email! Now THAT is how you serve your customers! 🤯
Adding these emails to your own ecommerce environment is easy with GRT for Email. Just compose your email in the GRT Email Editor, and then paste your output into the Text view of your ecommerce Plugin’s email editor:

Paste your GRT for Email output into the Text editor, and boom! Professional receipts 😮💨
If you don’t see a Text tab, look for a Source Code view, as seen here inside Digital Access Pass:

If you don’t have a Text editor, look for a way to edit Source Code 💡
Once inside the Source Code view, you can paste the GRT for Email output to create your emails.
Note: Every ecommerce Plugin I’ve used requires Universal output from GRT for Email.
Another pretty darn cool application for GRT for Email!