To add a confirmation checkbox with a description to your form:
Add a dropdown column to your board
Add only one option to the dropdown column, such as "I agree to the terms and conditions"
Add the new dropdown column to your form
Mark the field as required in Easyform so users will have to check it
Here's how to do steps 1 and 2:
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Here's how to do steps 3 and 4:
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Since field descriptions support HTML, you can add a link to an external page, such as your Terms & Conditions, by using the following HTML tag in the field description:
Adding a confirmation checkbox without a description
If you do not need to add a description to the confirmation box, you can just use a monday checkbox. First add the Checkbox column to your board and name it "Confirmation":
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Then, in the Easyform, add the confirmation checkbox to the form, set it to be required, and rename it to "I agree to the terms and conditions":