Login to ScalePrint Designer & Variants admin panel from your Shopify admin.
Select the "Product Custom options" from the left menu.
In the "Products" tab, click on the "Add Options" button for the product in which Checkbox Group custom option needs to be added. Please note if already have other options previously added to the product then click on the "Edit Options" button.
In the "Add Option" tab, click on the "Create new custom option" button.
From the "Create New Custom Option" dialog, enter the title for the custom option and from field type dropdown select the "Checkbox Group" option.
Enter the text for each of the checkbox that you want to add in the "Checkbox Group" custom option. Please note, any new checkbox can be added using the "Add New Item" button.
Click on the save button to save & add "Checkbox Group" to the product.
Optional fields: Create "Checkbox Group" dialog have following following optional fields that you can use as per your requirements - Help text, Description, Required (To make this field as required), Minimum number of selection (to add a condition for the user to check this much minimum checkbox), Maximum number of selection (to add a condition for the user to check maximum this much checkboxes)