Poker Keyword and 404

Hi, buddies
I have an interesting problem with wordpress, I have created a folder in wordpress root and there is a file add_post.php, this file post the data into wordpress.

I have a different interface for writers that write the articles in it. After writting the article they post it via add_post.php, this file get the data and make queries and add the content in wordpress tables. All is working fine but if there is a word like “poker” in content, it through 404 any clue?
url is like this: https://www.mywordpress.com/myfolder/add_news.php?title=poker&content=poker

When this url hist with “poker” keyword, it through the 404, other than this work fine.

Need urgent consultation

regards