Endpoint: www.youtube.com/youtubei/v1/next
Method: POST

Initial request:
{
    context: ...,

    playbackContext: {vis: 0, lactMilliseconds: "-1"},
    autonavState: "STATE_OFF",
    captionsRequested: false,
    videoId: iQfSvIgIs_M,
    contentCheckOk: false,
    racyCheckOk: false
}

Requesting comments / more recommendations:
{
    context: ...,

    # Continuation token from initial response
    continuation: "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",
}