To set up the ability to edit items in the cart, Shopify requires you to manually give the POS Cafe extension permission
Step 1
In your Shopify admin area, go to Sales Channels > Point of Sale > Settings in the left column, then choose POS app in the main window of the screen:
Step 2
On the next screen, click the app icon at the top , then enable POS Cafe:
Make sure to click Save at the top of the screen.
Step 3
You may need to resync your data in the Shopify POS app by tapping the connectivity icon, then Store data, and Refresh all:
To edit items in the cart, follow these steps:
Step 1
Tap on a POS Cafe item that has been added to the cart to open it's information pop up:
Step 2
A menu will slide up from beneath the cart. Tap POS Cafe:
Step 3
Edit your item as desired and tap Update Item: