Often the Internet Service Provider want a login, like PPPoE. As far as I know the beryl doesn’t provide such a login. At least within the GL.iNet frontend. Others just want a specific MAC, that is possible to provide f.ex. via MAC-Clone.
Maybe PPPoE can be installed from LuCI (advanced settings), or change the MAC without cloning.
But at first you need to know how to authenticate against your provider.