If WordPress adds a 2 to the end of your post or page URL (slug) and you have checked to make sure you don’t have a post of that name anywhere (including the trash!) then it could be because you uploaded an image of the same name. Let’s check:
- In the backend of WordPress, click on Media in the side menu.
- In the search field, search for the last part of the URL but remove the -2 (e.g. http://www.yourdomain.com/not-this/search-this-2/)
- If you find a matching image, click on it to open it up.
- Scroll to the bottom of the right column and click on “Edit more details” at the very bottom.
- At the top of the page under the title field click to edit the URL of the media attachment page.
- Change the URL.
- Click on the Update button.
There you go! You should now be able to go back to your post or page and edit the URL to remove the -2.