In some cases, for example, when you create an ad campaign there is no Instagram page available in the drop-down list on the Ads tab:
Most likely, your Instagram account isn't connected to the selected Facebook ad account, first, make sure you have added your Instagram profile to your Business Manager on Facebook.
If your Instagram page is already connected to your Business Manager check whether it is connected to any of your Facebook ad accounts where you have admin rights in:
3. If everything is properly connected we advise you to double-check Instagram
Is your Instagram page converted to Business Page? If so, follow the steps below:
Disconnect Instagram on the Integrations page
Make it a Personal account
Switch back to the Business account
Connect Instagram to Revealbot on the Integrations page.
4. You can also try to remove Revealbot app from Facebook and add it back again.
5. Next you can reconnect your Instagram account in the Integrations page in Revealbot.
Having the same trouble while creating a post-boosting rule? Check out this article to troubleshoot.