Possible 7 problems and fix for We're working on setting you up google AdSense home page

List of possible root causes of the Google Adsense still under review issue

1. Insufficient Content in the blog

Less number of posts and short length posts are not considered for Adsense approval. It may not contain detailed information to the readers or unable to give the ads for less content by Google Adsense or unable to index by Google. So these kinds of blogs are not taken into the approval process. A Blog at least should have 20 posts with good length 800 words. That is why AdSense having the standard waiting time about 6 months for newly created blogs to raise the AdSense request. If you have raised a request with minimal content, google will put the process under review stage.
Fix "Once you reached a good number of posts, cancel existing request and apply with new Adsense Account"

2. Copyrighted Content and Images

If blogs contain the posts or images that are already part of other websites or blogs or created by another author that has a copyright, then this is disapproved directly without telling any reason.
Fix "Remove all the copyrighted images immediately. blogs without images are also fine. Cancel existing AdSense request and reapply again"

3. Content Plagiarism

The blog contains duplicate content that is already available on other websites, blogs, social media is not acceptable. This is called plagiarism. A few lines or words in the posts are acceptable. But the complete content or huge chunk of content is matched with other sites are leading to content plagiarism. This is automatically detected by Google bot. 
Fix "If this is the case, remove the duplicated content else remove the complete posts or blog is the better option. Create a new blog and apply for Adsense with your own content"

4. Missing About, Privacy, Contact Pages

This could not the strict option. But sometimes this may considerable. This will increase the chances of AdSense approval. So having About, Privacy, Contact pages in your blog is always good for readers as well as AdSense application.

How to add privacy policy page in blogger?

5. Content Violation

Your content can be created by yourself. But It may contain abusive words, adult content, terrorism-related content. This content strictly unacceptable. 
Fix"Directly remove all the content or blogs"

6. More than an under review blog associated with same AdSense Account

This is a special case. You could have already raised the Google AdSense request for a blog. That may not meet the criteria and still under review. You could have raised another request to another blog with the same AdSense account. But the new one could be met with the criteria. You will be confused and thinking "This is a good blog. why it is still under review?"
Fix "Cancel the request first. If possible remove older blogs as it is no longer used by you. Then raise a new request with for latest blog with new AdSense account"

7. Already Disapprovaed blog associated with Google AdSense Account

This is also the same as the above case. You can follow the same fix

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