How to link single item with upsells/modifiers
Go to products
Click add new product and select modifier group.
Set the location to the master location, give it a name, set the minimum and maximum values that can be selected and add the products/modifiers in the group.
Adding items by entering the PLU works better than searching for the name.
Click ‘Save ‘
Go to the single item you where you want to link the modifier group and click on the right blue icon.
In this screen, you should be able to add the modifier group that you have created.
Adding the modifier group by the PLU works generally better.
Click ‘Save Edits’.
Go to your menu and you should see the modifier groups linked to the product.