Erro org.springframework.web.client.HttpServerErrorException: 500 null

org.springframework.web.client.HttpServerErrorException: 500 null
    org.springframework.web.client.DefaultResponseErrorHandler.handleError(DefaultResponseErrorHandler.java:94)
    org.springframework.web.client.RestTemplate.handleResponseError(RestTemplate.java:607)
    org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:565)
    org.springframework.web.client.RestTemplate.execute(RestTemplate.java:521)
    org.springframework.web.client.RestTemplate.postForObject(RestTemplate.java:321)
    org.casadocodigo.loja.controller.PagamentoController.lambda$finalizar$0(PagamentoController.java:37)
    org.springframework.web.context.request.async.WebAsyncManager$4.run(WebAsyncManager.java:322)
    java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
    java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
    java.base/java.lang.Thread.run(Thread.java:832)

package org.casadocodigo.loja.controller;

import org.casadocodigo.loja.models.CarrinhoCompras;
import org.casadocodigo.loja.models.CarrinhoItem;
import org.casadocodigo.loja.models.DadosPagamento;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.client.HttpClientErrorException;
import org.springframework.web.client.RestTemplate;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.support.RedirectAttributes;

import java.util.concurrent.Callable;

@RequestMapping("/pagamento")
@Controller
@Scope(value = WebApplicationContext.SCOPE_REQUEST)
public class PagamentoController {

    @Autowired
    private CarrinhoCompras carrinho;

    @Autowired
    private RestTemplate restTemplate;

    @RequestMapping(value="/finalizar", method=RequestMethod.POST)
    public Callable<ModelAndView> finalizar(RedirectAttributes model){

        return () -> {
            String uri = "http://book-payment.herokuapp.com/payment";

            try {
                String response = restTemplate.postForObject(uri,
                        new DadosPagamento(carrinho.getTotal()), String.class);
                model.addFlashAttribute("sucesso", response);
                System.out.println(response);
                return new ModelAndView("redirect:/produtos");
            } catch (HttpClientErrorException e) {
                e.printStackTrace();
                model.addFlashAttribute("falha", "Valor maior que o permitido");
                return new ModelAndView("redirect:/produtos");
            }
        };

    }
}

@Bean
    public RestTemplate restTemplate (){
        return new RestTemplate();
    }