If you would like ads created in Ads Manager to be posted on Instagram as well as Facebook, you'll first need to connect the two accounts. Follow the instructions below.
1. Go to Your Facebook Business Page Settings
Navigate to your Facebook Business Page and click "Settings."
2. Click "Instagram"
From the left-hand toolbar under Page Settings, scroll down and click "Instagram."
3. Click "Connect Account"
On the next page, click "Connect Account."
Follow the remaining screens provided by Facebook to complete the process.
Learn more about connecting Facebook and Instagram from the Facebook Help Center.
If you're already in the process of editing an ad within Facebook, you can also connect your Instagram page directly within the ads dashboard. Simply click "Connect Account" in the panel shown below.
Once your Facebook and Instagram accounts are connected, you'll be able to set specific ads to post to Instagram. This is done on an ad-by-ad basis. Learn how here. (Link coming soon!)