Update Currency Warning

src/main/java/org/prebid/server/auction/BidsAdjuster.java

@@ -95,8 +95,9 @@ private AuctionParticipation validBidderResponse(AuctionParticipation auctionPar
 
         final List<String> requestCurrencies = bidRequest.getCur();
         if (requestCurrencies.size() > 1) {
-            errors.add(BidderError.badInput("Cur parameter contains more than one currency. %s will be used"
-                    .formatted(requestCurrencies.getFirst())));
+            warnings.add(BidderError.badInput(
+                    "a single currency (" + requestCurrencies.getFirst() + ") has been chosen for the request. "
+                            + "ORTB 2.6 requires that all responses are in the same currency."));
         }
 
         final List<BidderBid> bids = seatBid.getBids();
@@ -118,9 +119,7 @@ private AuctionParticipation validBidderResponse(AuctionParticipation auctionPar
             }
         }
 
-        final BidderResponse resultBidderResponse = errors.size() == seatBid.getErrors().size()
-                ? bidderResponse
-                : bidderResponse.with(
+        final BidderResponse resultBidderResponse = bidderResponse.with(
                 seatBid.toBuilder()
                         .bids(validBids)
                         .errors(errors)

src/test/groovy/org/prebid/server/functional/tests/CurrencySpec.groovy

@@ -14,6 +14,7 @@ import static org.prebid.server.functional.model.Currency.CHF
 import static org.prebid.server.functional.model.Currency.EUR
 import static org.prebid.server.functional.model.Currency.JPY
 import static org.prebid.server.functional.model.Currency.USD
+import static org.prebid.server.functional.model.response.auction.ErrorType.GENERIC
 import static org.prebid.server.functional.testcontainers.Dependencies.networkServiceContainer
 
 class CurrencySpec extends BaseSpec {
@@ -146,6 +147,49 @@ class CurrencySpec extends BaseSpec {
         CHF             || EUR
     }
 
+    def "PBS should emit warning when request contain more that one currency"() {
+        given: "Default BidRequest with currencies"
+        def currencies = [EUR, USD]
+        def bidRequest = BidRequest.defaultBidRequest.tap {
+            cur = currencies
+        }
+
+        when: "PBS processes auction request"
+        def bidResponse = pbsService.sendAuctionRequest(bidRequest)
+
+        then: "Bid response should contain first requested currency"
+        assert bidResponse.cur == currencies[0]
+
+        and: "Bidder request should contain requested currencies"
+        def bidderRequest = bidder.getBidderRequest(bidRequest.id)
+        assert bidderRequest.cur == currencies
+
+        and: "Bid response should contain warnings"
+        assert bidResponse.ext.warnings[GENERIC]?.message == ["a single currency (${currencies[0]}) has been chosen for the request. " +
+                "ORTB 2.6 requires that all responses are in the same currency." as String]
+    }
+
+    def "PBS shouldn't emit warning when request contain one currency"() {
+        given: "Default BidRequest with currency"
+        def currency = [USD]
+        def bidRequest = BidRequest.defaultBidRequest.tap {
+            cur = currency
+        }
+
+        when: "PBS processes auction request"
+        def bidResponse = pbsService.sendAuctionRequest(bidRequest)
+
+        then: "Bid response should contain first requested currency"
+        assert bidResponse.cur == currency[0]
+
+        and: "Bidder request should contain requested currency"
+        def bidderRequest = bidder.getBidderRequest(bidRequest.id)
+        assert bidderRequest.cur == currency
+
+        and: "Bid response shouldn't contain warnings"
+        assert !bidResponse.ext.warnings
+    }
+
     private static Map<String, String> getExternalCurrencyConverterConfig() {
         ["auction.ad-server-currency"                          : DEFAULT_CURRENCY as String,
          "currency-converter.external-rates.enabled"           : "true",

src/test/java/org/prebid/server/auction/BidsAdjusterTest.java

@@ -332,7 +332,7 @@ public void shouldRespondWithOneBidAndErrorWhenBidResponseContainsOneUnsupported
     }
 
     @Test
-    public void shouldUpdateBidPriceWithCurrencyConversionAndAddErrorAboutMultipleCurrency() {
+    public void shouldUpdateBidPriceWithCurrencyConversionAndAddWarningAboutMultipleCurrency() {
         // given
         final BigDecimal bidderPrice = BigDecimal.valueOf(2.0);
         final BidderResponse bidderResponse = BidderResponse.of(
@@ -363,14 +363,16 @@ public void shouldUpdateBidPriceWithCurrencyConversionAndAddErrorAboutMultipleCu
 
         assertThat(result).hasSize(1);
 
-        final BidderError expectedError = BidderError.badInput("Cur parameter contains more than one currency."
-                + " CUR1 will be used");
         final BidderSeatBid firstSeatBid = result.getFirst().getBidderResponse().getSeatBid();
         assertThat(firstSeatBid.getBids())
                 .extracting(BidderBid::getBid)
                 .flatExtracting(Bid::getPrice)
                 .containsOnly(updatedPrice);
-        assertThat(firstSeatBid.getErrors()).containsOnly(expectedError);
+
+        final BidderError expectedWarning = BidderError.badInput(
+                "a single currency (CUR1) has been chosen for the request. "
+                        + "ORTB 2.6 requires that all responses are in the same currency.");
+        assertThat(firstSeatBid.getWarnings()).containsOnly(expectedWarning);
     }
 
     @Test