Should I use a User access token or a System User access token when configuring the Facebook Messenger channel in Conversation API?

When connecting your Facebook Page to your Conversation API app you must use either a User access token or a System User access token. 

If your Facebook Page is part of your business portfolio in the Meta Business Manager, you must connect your Page using the System User access token option. If your Page is not part of a business portfolio, use the User access token option.