Hello Alexander,
Thank you for reaching out to us.
When using checkboxes in the Form Builder, you need to add checkbox item option in the form field. When editing the checkbox, you will see a “field name” for each checkbox item. You can then use this field name in your email template to display the selected options. For example, you can use {{checkbox-1}}{{checkbox-2}} to refer to the checkbox field in the email. If you have multiple choices for the same checkbox, use the different field name for both and use it like example.
Thank you!