BOMA posts to Instagram only in paid social advertising, not organic posts.
Instagram is connected to BOMA via Facebook so you'll need to ensure your Instagram and Facebook page are connected.
To add an existing Instagram account to your Facebook Page:
Go to your Facebook Page.
Click Settings in the top-right of your Page.
Click Instagram Ads.
To add an existing Instagram account to your Page, click Add an Account.
Enter your Instagram account's Username and Password, and click Confirm.
Now you can add Instagram to BOMA. Go to Settings then Social Media. If you already have Facebook connected, disconnect it. Then connect your Facebook and BOMA will connect Facebook (and your Facebook connected) Instagram accounts.
Now you're ready to post an Instagram ad.