This is how to fix mainEntityofPage warning in Blogger site.
When you check with Google Structured Data Testing Tool, you might see this remark in orange color:
mainEntityofPage The mainEntityofPage field is recommended. Please provide a value if available.
It is not a serious structured data error, it's just a warning.
Anyway, you should have this mainEntityofPage warning removed, if you want a better meta description in the search engine results page.
It is not that difficult to solve this structured data markup issue.
This is another how-to tutorial from the DiGiztal Blogspot Blogger Tips series.
Remove mainEntityofPage warning in Blogger
Let me show you how it is done:
1. Sign into your Blogger account.
2. Click "Theme".
3. Then click "Edit HTML".
4. Look for this line of code:
<div class='post hentry uncustomized-post-template' itemprop='blogPost' itemscope='itemscope' itemtype='http://schema.org/BlogPosting'>
NOTE: If you CANNOT find the above code, then look for this:
<div class='post hentry' itemprop='blogPost' itemscope='itemscope' itemtype='http://schema.org/BlogPosting'>
5. Delete it away the either one of code as shown above.
6. Replace it with this:
<div class='post hentry uncustomized-post-template' itemscope='itemscope' itemtype='http://schema.org/BlogPosting'>
<meta itemscope='itemscope' itemprop='mainEntityOfPage' itemType='https://schema.org/WebPage' expr:itemid='data:post.link ? data:post.link : data:post.url'/>
NOTE: There are TWO sets of the same code that need to be replaced.
In other words, after you have done the first one, look for another same set of the same code and replace it too.
7. Then click on "Save theme".
8. That's all.