Rails and Webmotors

Anyone with any experience with Rails integration with the Webmotors APi?

I am using the gem SAVON to integrate the application with the site API and I am getting the error:

Soap:: SOAPFault: (soap: Server) Server was unable to process request. --- >Object reference not set to an instance of an object.

What I'm doing is:

def self.login_webmotors
      cnpj = "xxxxxxxxxx"
      email = "xxxxxxxx"
      senha = "xxxxxxxx"
      #wdsl_add = 'http://www.webmotors.com.br/IntegracaoRevendedor/wsEstoqueRevendedorWebMotors.asmx?WSDL'
      login_url = 'http://www.webmotors.com.br/IntegracaoRevendedor/wsLoginSistemaRevendedor.asmx?WSDL'
      login = Savon.client(wsdl: login_url,
                                log: true,
                                log_level: :debug,
                                pretty_print_xml: true)

      response = login.call(:autenticar, message: { cnpj: cnpj, email: email, senha: senha })

      Rails.application.config.hash_webmotors = response.body[:autenticar_response][:autenticar_result][:hash_autenticacao]

      Savon.client(headers: { "hash_autenticacao" => Rails.application.config.hash_webmotors })
    end

And then:

def self.adicionar_carro
    login_webmotors

    wDSL = 'http://www.webmotors.com.br/IntegracaoRevendedor/wsEstoqueRevendedorWebMotors.asmx?WSDL'

    add = Savon.client(wsdl: wDSL,
                            log: true,
                            log_level: :debug,
                            pretty_print_xml: true)

    message = { codigo_anuncio: 1234, 
                codigo_modalidade: 1, 
                tipo_anuncio: "teste", 
                codigo_marca: 1, 
                codigo_modelo: 1, 
                codigo_versao: 1, 
                ano_modelo: 2000, 
                ano_fabricacao: 1995, 
                km: 20000, 
                placa: "pg1234", 
                codigo_cambio: 1  }

    carro = add.call(:incluir_carro, message: message )
end

But I always bump into the same error

Soap:: SOAPFault: (soap: Server) Server was unable to process request. --- >Object reference not set to an instance of an object.