There are a few reasons why your ad may not appear immediately on the OE ADS platform and could have possibly been removed. This depends on a few things like:

You have violated our OE ADS Rules
You have posted a service or Items Not allowed
Users flagged the ad as being spam or offensive
The ad expired automatically after being listed for its full duration.
Your ad has been reported to us and your access has been restricted
To ensure your ad does not get the boot, have a look at these most common reasons why your ad could have possibly been removed:

Posting duplicate ads are not cool and a definite no-go on OE ADS. If you post multiple items or even in multiple locations, your ads will be removed and could lead to your access being restricted.
We do not allow URLs /Emails/ Unverified Phone numbers in the title or description of your ad, however, you may add a URL in the description of your ad as long as it’s a link to additional information or to a page with more pictures. We do not allow links that are designed solely to redirect traffic to another website.
Make sure the price of your item does not exceed or go drastically below the secondary market value.
If you post an offer for formal employment, we prefer you to use an active, legitimate business domain. You will be able to use your personal email address if you’re posting an ad as a private individual looking to hire a nanny or domestic help.
Remember, your photos need to be relevant and appropriate. Bathroom or bedroom selfies are not nice!