gem Faraday Error `undefined method `bytesize' for Hash`

Question

I want to POST request, using Ruby gem Faraday. Content-Type is "application/pdf".

my code is below.

    client = Faraday.new(endpoint) do |client|
      client.request :retry
      client.headers['Content-Type'] = "application/pdf"
      client.headers['Authorization'] = auth_token
      client.adapter Faraday.default_adapter
    end

    response = client.public_send(:post, endpoint, params)

but, I got Error.

undefined method `bytesize' for {:title=>"0722 14 ID:14"}:Hash

Please Help me.