Refreshing the token using Timdorr's Ruby classes

[BlackPhoenix]

I am using the the "Quick Example" from the main page, with a slight modification to refresh the token: I added the following at the end:

puts "Refreshing token..."

tesla_api.refresh_access_token
puts tesla_api.access_token
puts tesla_api.refresh_token
puts tesla_api.access_token_expires_at

I get this:

Your Model S is Disconnected with a SOC of 63% and an estimate range of 157.86 miles
Refreshing token...
/home/black/.gem/ruby/2.6.0/gems/faraday-1.4.2/lib/faraday/response/raise_error.rb:16:in `on_complete': the server responded with status 400 (Faraday::BadRequestError)
	from /home/black/.gem/ruby/2.6.0/gems/faraday-1.4.2/lib/faraday/middleware.rb:19:in `block in call'
	from /home/black/.gem/ruby/2.6.0/gems/faraday-1.4.2/lib/faraday/response.rb:59:in `on_complete'
	from /home/black/.gem/ruby/2.6.0/gems/faraday-1.4.2/lib/faraday/middleware.rb:18:in `call'
	from /home/black/.gem/ruby/2.6.0/gems/faraday_middleware-1.0.0/lib/faraday_middleware/response_middleware.rb:36:in `call'
	from /home/black/.gem/ruby/2.6.0/gems/faraday_middleware-1.0.0/lib/faraday_middleware/request/encode_json.rb:26:in `call'
	from /home/black/.gem/ruby/2.6.0/gems/faraday-1.4.2/lib/faraday/rack_builder.rb:154:in `build_response'
	from /home/black/.gem/ruby/2.6.0/gems/faraday-1.4.2/lib/faraday/connection.rb:494:in `run_request'
	from /home/black/.gem/ruby/2.6.0/gems/faraday-1.4.2/lib/faraday/connection.rb:279:in `post'
	from /home/black/.gem/ruby/2.6.0/gems/tesla_api-3.1.0/lib/tesla_api/client.rb:45:in `refresh_access_token'

My access token is obviously valid: the code can tell my SOC is 63%. But I get HTTP 400 when calling the refresh_access_token method. The library is what is currently in GitHub. Did I miss something obvious?