Under "Items & Services" click on the "Modifiers" tab.
On the Modifiers page, click on the "Add new" button on the top right. You will be
prompted with a pop-up window to create your modifier.
After entering the name of your modifier (e.g., “Size”), use the "Must select one" toggle to indicate whether the modifier is required. Then, in the "Select Limit" section, specify the minimum or maximum number of options that must be selected.
Next, if applicable, add the modifier options (e.g., “Large,” “Medium,” “Small”) by entering each one in the "New Modifier" text field.