1. Ensure you have an Instagram business account that is connected to a Facebook Page
If you don't have one or are not sure, please follow the instructions below.
How to set up a business account on InstagramAdd a Facebook Page to your Instagram Business Account
2. Enable the automated messaging feature on Instagram
Follow the instructions below to enable this feature which will allow you to send and receive IG DMs from your unified inbox.
How to enable automated messaging
3. Follow the on-screen prompt on the Settings page (bottom left) of your Inbox and click "Login with Facebook" [red button]
This will automatically transfer your to Facebook, where you will find step-by-step instructions to connect your Instagram account. You will need to accept all permissions.