As of 2020-11-25 The syntax of channel.push(...) should be updated to include a second parameter.
As written the book states on page 47:

channel.push("ping")
    .receive(...)

This causes an error that precedes and prevents joining the channel in addition to preventing the reception of any messages back from the server:

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A slight modification allows success:

channel.push("ping", {})
    .receive(...)

This error is likely due to a contract change in the Phoenix channel library.