Primary menu item is not highlighting when page is active even though it is linked from a url with query string to pre-populate a form field

I checked both of your links and in the <body> tag, both of them have class page-id-1508, meaning that the page id is recognised correctly either with or without the query variable.

However, as @mmm suggested in the comment above, it seems that you added the menu item as Custom Link (note the menu item classes menu-item-type-custom menu-item-object-custom; if you added it as a Page, it would has classes menu-item-type-post_type menu-item-object-page).

Since it is a Custom Link, when the link changes (in this case, it has query variable added), WordPress doesn’t recognise it as the same link anymore, and thus it looses the active class.

So because that is a page, I suggest you add that menu item as a page and check again.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)