The "Houbi" app allows you to invite other users to your group.
Open the Store and make sure the app is up to date. Please update the app if there is an update.
Display the invitation QR code from [Member icon in Home > Invite an user to this group > Show Invitation QR Code].
Read the invitation QR code from [Start > Read QR Code].
You can scan the QR code by tapping [Group icon (rounded square icon) in the top right of the home page > + Add group > Join existing group > Read QR code].