How to fix
Duplicate without user-selected canonical issue
Short : Add a link tag with rel="canonical"
You will get this issue if you have / google detect more than one page with same content and different urls.
You can fix it by adding a link tag in your duplicate pages with
rel="canonical" attribute and
href pointing to original page or page which you want to appear on search.
<link rel="canonical" href="[url of original page / page which you want to appear on search]">