Missing field “mainEntity” on Q2A

Hi Q2A webmasters!
Today I go to Google Search Console , I've found an error message with my question2answer website: Missing field "mainEntity"
I follow the instructions from the official website: https://www.question2answer.org/qa/70061/schema-org-errors-mainentity-missing . But it didn't work. My Q2A app version is 1.8.3, It must work well.
But, I suddenly check my current QA-theme, the version is too old. I browse the website on Google Chrome, using debug windows (F12 function ). I tried to find the keyword "mainEntiy", there's no result return.
So I got the key,just update my qa-theme: qa-theme/my-customized-theme/qa-theme.php :
Find:
$this->output('<DIV CLASS="qa-body-wrapper"', '');

Replace by:
$this->output('<DIV CLASS="qa-body-wrapper" itemprop="mainEntity" itemscope itemtype="https://schema.org/Question">', '');

Now re-submit the fixing error to Search Console.