As noted in the section Considerations for Using Peer-to-Peer Replication in Peer-to-Peer Transactional Replication, subscriptions must be initialized by using a backup or with the replication support only option.
Subscriptions must be initialized by using a backup or with the 'replication support only' option. For more information, see Initialize a Transactional Subscription Without a Snapshot.
You are currently attempting to initialize Peer-to-Peer subscription with a snapshot (sync_type automatic) using the New Subscription Wizard which is not allowed.
I suggest using the Configure Peer-to-Peer Topology Wizard to add new peer nodes to your topology. Instructions on how to use the Configure Peer-to-Peer Topology Wizard to configure your Peer-to-Peer topology can be found in How to: Configure Peer-to-Peer Transactional Replication (SQL Server Management Studio).
Alternatively, you can configure your Peer-to-Peer topology using T-SQL which is covered in How to: Configure Peer-to-Peer Transactional Replication (Replication Transact-SQL Programming).