Page post engagement is a great way to gain likes, comments and shares on your Facebook posts. You can create a post ad as a video, photo or text to engage your users. To do so, click on the “Build Audience” at the top right corner of your Facebook page and click “Use Ads Manager”. Click on the green button “Create Ad” and click “Page Post Engagement” from the list. From there, you can select which post you’d like to promote, target your audience and set a campaign pricing. It will take a few minutes for your ad to be approved.
For video ads, it is recommended to use 500 characters of text, 16:9 aspect ratio, 1080 resolution, .mov file format and no larger than 1 gigabyte. An example of what a video ad may look like on desktop, mobile and right side of Facebook:

For photo ads, it is recommended to use 90 characters of text, 1:1 image ratio (a perfect squared image) and 1200×1200 pixels image. Furthermore there is a 20% limit to how much text can be added in your photo. Having too much text in your photo will get your ad disapproved. You should use the Facebook grid tool to see how much text is being used on your photo: https://www.facebook.com/ads/tools/text_overlay. Here are what photo ads look like on desktop, mobile and right side of Facebook:

For text ads, it is recommended to use 90 characters of text. Here are what text ads look like on desktop, mobile and right side of Facebook: