When you try to convert to a business account, you may get a message from Instagram saying your account already belongs to a Facebook account.
This happens because the Facebook page is linked to a personal Instagram account.
The simplest way to fix this up is to:
- Unlink personal Instagram account from the Facebook Page
- Change to business Instagram account
- Re-link to Facebook page
If you're still having any problems, please visit the Instagram / Facebook troubleshooting page for help reconnecting your account.