[fix/#56] 에러 해결을 위한 로그

Author: hyowon0204

src/main/java/com/sumte/payment/kakaopay/KakaoPayClient.java

@@ -6,12 +6,16 @@
 import com.sumte.payment.dto.KakaoPayReadyRequestDTO;
 import com.sumte.payment.dto.KakaoPayReadyResponseDTO;
 import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
 import org.springframework.beans.factory.annotation.Value;
+import org.springframework.http.HttpStatusCode;
 import org.springframework.stereotype.Component;
 import org.springframework.web.reactive.function.client.WebClient;
+import reactor.core.publisher.Mono;
 
 @Component
 @RequiredArgsConstructor
+@Slf4j
 public class KakaoPayClient {
 
     private final WebClient webClient;
@@ -27,6 +31,12 @@ public KakaoPayReadyResponseDTO requestPayment(KakaoPayReadyRequestDTO request)
                 .header("Content-Type", "application/json")
                 .bodyValue(request)
                 .retrieve()
+                .onStatus(HttpStatusCode::isError, res ->
+                        res.bodyToMono(String.class).flatMap(body -> {
+                            log.info("KakaoPay READY {} body: {}", res.statusCode(), body); // 핵심!
+                            return Mono.error(new IllegalStateException("KakaoPay ready error: " + body));
+                        })
+                )
                 .bodyToMono(KakaoPayReadyResponseDTO.class)
                 .block();
     }