Oftentimes, posts are rejected due to the content of the post, the photo/image being used, or if the business is in a “sensitive” topics area. Sometimes words within the post will trigger a post rejection. The word may seem benign, but it may be on Google’s “offensive” word list (rejected posts are controlled on Google’s end and not Social Marketing). If your post gets rejected, try re-wording to a more generic body copy, and don’t include any sensitive words or images. Also, it used to be acceptable to include your phone number or a website URL in the body of a post. Google is now rejecting many posts with phone numbers or URLs. So if your post is rejected, try taking those elements out”. Google Posts are also not permitted for multi-location chain businesses. 

Learn more here: https://www.searchenginejournal.com/google-my-business-common-problems/381328/#close