Facebook has officially announced that the cross-service messaging feature between Instagram and Facebook Messenger is now available for group chats as well. In other words, you can create an Instagram correspondence with users who only have Facebook - and vice versa.
To do this, the inviting user must have cross-service messaging enabled in both apps. Both Messenger and Instagram will prompt you to turn it on the first time you sign in to your account after the update, and you can also enable synchronization manually.
To do this, in the settings of both applications, there is a section "Account Center", which allows you to synchronize profiles in different social networks. After that, when you create a chat in one service, you will see the opportunity to invite your friends or followers from the other.
Users can still limit the list of people who can invite them into chats: this setting will also apply to cross-platform invitations.
The update is rolling out gradually and may not be available to everyone. It's also worth making sure you have the latest version of both apps installed.