Validate fields if checkbox is not checked

Hi, i would like validate with "required" some fields only if checkbox is not checked.
https://drive.google.com/file/d/1BIFWo1C...sp=sharing
Is possible? How can i do?

I thought which i could change checkbox in a dropdown and validate others fields only if has been selected a specific value from dropdown (in my case value 2).

PHP Code:

<select name="shipping-method">
<option value="1">pickup in store</option>
<option value="2">courier service</option>
</select> 


This solution could be more easy? Any suggestion for me? Thanks.