Display text field after checkbox

You can use Field Rules for this purpose.

In your wp-admin go to Fields Factory -> Product Fields in that page click on the fields group (which ever group has the check box & text field).

Now click on the Checkbox field (which you have already created), now you will be shown the field config view.

There you can see three tabs (Field Meta, Pricing Rules & Field Rules), click on the Field Rules

Now click on the Add Field Rule button, now choose Checkedoption from the select box and check the below check box (whichever needs the checked rule).

On the right side choose the “Show” for the text box.

Now click on Add Field Rule again and do the same for the Unchecked

Let me know if you have any issue.

Works great
Thank you