Firstly, you need an Instagram business account. To change from personal account to business account, follow steps 1, 2 and 3 in the following screenshot and choose "Business":
Then connect your Instagram business account with your Facebook page. A Facebook page is a must, if you don't have one, create a new page.
Go to the "Settings" of your Facebook page, then "Instagram", "Connect Account".
The next step is to turn on the "Allow access to messages" in your Instagram app, see steps 1 to 5 in the following screenshot: Menu - Settings - Privacy - Messages - Allow access to messages
Finally, in OCP, let's connect your Instagram with OCP. Go "Facebook" and "Reconnect" (Yes, Facebook, not Instagram):
Continue as yourself or click "Edit Settings" if you've previously linked to your Facebook.
Give all permissions and after the connection, you are able to see your Instagram flow in both "Facebook" and "Instagram":
Instagram doesn't support Preview feature, so to talk to your Instagram bot:
Search your account name on Instagram or go to the Instagram section on OCP dashboard, click on the URL link below the bot name to visit your Instagram page
follow the account and click Message to start the conversation.