CF7 set Dynamic Default values for CHECKBOX

See Editing Form Template

What form template do you have in the Form tab panel?

I wanna make only that particular option selected related to the page visited by user. like if user is at page-3 thn optin-3 should be active by default and so on….

form will be like this: https://paste.pics/7S9B5
contact form code is like this: https://paste.pics/7S99E
shortcode used as: https://paste.pics/7S99T
function added to function.php is: https://paste.pics/7S9AF

this is working fine on text field but I want it with checkbox

Try setting the shortcode attribute with the value, like this:

[contact-form-7 id="7" title="Contact form 1" checkbox-246="Option 2"]

works perfectly ?? – thanks