Instagram Inbox
How to connect an Instagram inbox
Go to the Connect Platform page
Open the Connect Platform page from the navbar or the Settings menu.

Click the plus button to add a new inbox or platform
Click the "+" button to the right of Inboxes to add a new inbox or platform.

Choose Instagram
Select the Instagram option.

Log in to your Instagram account
Enter your Instagram login details. Make sure the account is public, not private.
Give business access permission
Allow Instagram to access your current and future businesses, then click Continue.
Choose your accounts
Select the Facebook Page and the Instagram account you want to connect, then click Continue.
Finish the setup
Click Continue, then Done.
Check your connected inbox
Go back to Connected Platform to make sure everything is connected.
Your Instagram inbox will appear there, ready to use.