Adding support for Get App Transaction Info endpoint

src/main/java/com/apple/itunes/storekit/client/APIError.java

@@ -496,6 +496,13 @@ public enum APIError {
      */
     MESSAGE_NOT_FOUND(4040015L),
 
+    /**
+     * An error response that indicates an app transaction doesn’t exist for the specified customer.
+     *
+     * @see <a href="https://developer.apple.com/documentation/appstoreserverapi/apptransactiondoesnotexisterror">AppTransactionDoesNotExistError</a>
+     */
+    APP_TRANSACTION_DOES_NOT_EXIST_ERROR(4040019L),
+
     /**
      * An error that indicates the image identifier already exists.
      *

src/main/java/com/apple/itunes/storekit/client/BaseAppStoreServerAPIClient.java

@@ -2,6 +2,7 @@
 
 package com.apple.itunes.storekit.client;
 
+import com.apple.itunes.storekit.model.AppTransactionInfoResponse;
 import com.apple.itunes.storekit.model.CheckTestNotificationResponse;
 import com.apple.itunes.storekit.model.ConsumptionRequest;
 import com.apple.itunes.storekit.model.DefaultConfigurationRequest;
@@ -485,6 +486,19 @@ public void deleteDefaultMessage(String productId, String locale) throws APIExce
         makeHttpCall("/inApps/v1/messaging/default/" + productId + "/" + locale, "DELETE", Map.of(), null, Void.class, null);
     }
 
+    /**
+      * Get a customer’s app transaction information for your app.
+      *
+      * @param transactionId Any originalTransactionId, transactionId or appTransactionId that belongs to the customer for your app.
+      * @return A response that contains signed app transaction information for a customer.
+      * @throws APIException If a response was returned indicating the request could not be processed.
+      * @throws IOException  If an exception was thrown while making the request.
+      * @see <a href="https://developer.apple.com/documentation/appstoreserverapi/get-app-transaction-info">Get App Transaction Info</a>
+      */
+     public AppTransactionInfoResponse getAppTransactionInfo(String transactionId) throws APIException, IOException {
+         return makeHttpCall("/inApps/v1/transactions/appTransactions/" + transactionId, "GET", Map.of(), null, AppTransactionInfoResponse.class, null);
+     }
+
     protected interface HttpResponseInterface extends Closeable {
         /**
          * @return The HTTP status code of the response

src/main/java/com/apple/itunes/storekit/model/AppTransactionInfoResponse.java

@@ -0,0 +1,89 @@
+// Copyright (c) 2025 Apple Inc. Licensed under MIT License.
+
+package com.apple.itunes.storekit.model;
+
+import com.fasterxml.jackson.annotation.JsonAnySetter;
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+import java.util.Map;
+import java.util.Objects;
+
+/**
+ * A response that contains signed app transaction information for a customer.
+ *
+ * @see <a href="https://developer.apple.com/documentation/appstoreserverapi/apptransactioninforesponse">AppTransactionInfoResponse</a>
+ */
+public class AppTransactionInfoResponse {
+    private static final String SERIALIZED_NAME_SIGNED_APP_TRANSACTION_INFO = "signedAppTransactionInfo";
+
+    @JsonProperty(SERIALIZED_NAME_SIGNED_APP_TRANSACTION_INFO)
+    private String signedAppTransactionInfo;
+    @JsonAnySetter
+    private Map<String, Object> unknownFields;
+
+    public AppTransactionInfoResponse() {
+    }
+
+    public AppTransactionInfoResponse signedAppTransactionInfo(String signedAppTransactionInfo) {
+        this.signedAppTransactionInfo = signedAppTransactionInfo;
+        return this;
+    }
+
+    /**
+     * A customer’s app transaction information, signed by Apple, in JSON Web Signature (JWS) format.
+     * 
+     * @return signedAppTransactionInfo
+     * @see <a href="https://developer.apple.com/documentation/appstoreserverapi/jwsapptransaction">JWSAppTransaction</a>
+     **/
+    public String getSignedAppTransactionInfo() {
+        return signedAppTransactionInfo;
+    }
+
+    public void setSignedAppTransactionInfo(String signedAppTransactionInfo) {
+        this.signedAppTransactionInfo = signedAppTransactionInfo;
+    }
+
+    public AppTransactionInfoResponse unknownFields(Map<String, Object> unknownFields) {
+        this.unknownFields = unknownFields;
+        return this;
+    }
+
+    /**
+     * Fields that are not recognized for this object.
+     * 
+     * @return A map of JSON keys to objects.
+     */
+    public Map<String, Object> getUnknownFields() {
+        return unknownFields;
+    }
+
+    public void setUnknownFields(Map<String, Object> unknownFields) {
+        this.unknownFields = unknownFields;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        AppTransactionInfoResponse that = (AppTransactionInfoResponse) o;
+        return Objects.equals(this.signedAppTransactionInfo, that.signedAppTransactionInfo) &&
+                Objects.equals(this.unknownFields, that.unknownFields);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(signedAppTransactionInfo, unknownFields);
+    }
+
+    @Override
+    public String toString() {
+        return "AppTransactionInfoResponse{" +
+                "signedAppTransactionInfo='" + signedAppTransactionInfo + '\'' +
+                ", unknownFields=" + unknownFields +
+                '}';
+    }
+}

src/test/java/com/apple/itunes/storekit/client/AppStoreServerAPIClientTest.java

@@ -3,6 +3,7 @@
 package com.apple.itunes.storekit.client;
 
 import com.apple.itunes.storekit.model.AccountTenure;
+import com.apple.itunes.storekit.model.AppTransactionInfoResponse;
 import com.apple.itunes.storekit.model.CheckTestNotificationResponse;
 import com.apple.itunes.storekit.model.ConsumptionRequest;
 import com.apple.itunes.storekit.model.ConsumptionStatus;
@@ -913,6 +914,68 @@ public void testTransactionIdNotOriginalTransactionId() throws IOException {
         Assertions.fail();
     }
 
+    @Test
+     public void testGetAppTransactionInfo() throws APIException, IOException {
+         AppStoreServerAPIClient client = getClientWithBody("models/appTransactionInfoResponse.json", request -> {
+             Assertions.assertEquals("GET", request.method());
+             Assertions.assertEquals("/inApps/v1/transactions/appTransactions/1234", request.url().encodedPath());
+             Assertions.assertNull(request.body());
+         });
+
+         AppTransactionInfoResponse appTransactionInfoResponse = client.getAppTransactionInfo("1234");
+
+         Assertions.assertNotNull(appTransactionInfoResponse);
+         Assertions.assertEquals("signed_app_transaction_info_value", appTransactionInfoResponse.getSignedAppTransactionInfo());
+     }
+
+     @Test
+     public void testGetAppTransactionInfoInvalidTransactionIdError() throws IOException {
+         String body = TestingUtility.readFile("models/invalidTransactionIdError.json");
+         AppStoreServerAPIClient client = getAppStoreServerAPIClient(body, request -> {}, 400);
+         try {
+             client.getAppTransactionInfo("invalid_transaction_id");
+         } catch (APIException e) {
+             Assertions.assertEquals(400, e.getHttpStatusCode());
+             Assertions.assertEquals(APIError.INVALID_TRANSACTION_ID, e.getApiError());
+             Assertions.assertEquals(4000006L, e.getRawApiError());
+             Assertions.assertEquals("Invalid transaction id.", e.getApiErrorMessage());
+             return;
+         }
+         Assertions.fail();
+     }
+
+     @Test
+     public void testGetAppTransactionInfoAppTransactionDoesNotExistError() throws IOException {
+         String body = TestingUtility.readFile("models/appTransactionDoesNotExistError.json");
+         AppStoreServerAPIClient client = getAppStoreServerAPIClient(body, request -> {}, 404);
+         try {
+             client.getAppTransactionInfo("nonexistent_transaction_id");
+         } catch (APIException e) {
+             Assertions.assertEquals(404, e.getHttpStatusCode());
+             Assertions.assertEquals(APIError.APP_TRANSACTION_DOES_NOT_EXIST_ERROR, e.getApiError());
+             Assertions.assertEquals(4040019L, e.getRawApiError());
+             Assertions.assertEquals("No AppTransaction exists for the customer.", e.getApiErrorMessage());
+             return;
+         }
+         Assertions.fail();
+     }
+
+     @Test
+     public void testGetAppTransactionInfoTransactionIdNotFoundError() throws IOException {
+         String body = TestingUtility.readFile("models/transactionIdNotFoundError.json");
+         AppStoreServerAPIClient client = getAppStoreServerAPIClient(body, request -> {}, 404);
+         try {
+             client.getAppTransactionInfo("not_found_transaction_id");
+         } catch (APIException e) {
+             Assertions.assertEquals(404, e.getHttpStatusCode());
+             Assertions.assertEquals(APIError.TRANSACTION_ID_NOT_FOUND, e.getApiError());
+             Assertions.assertEquals(4040010L, e.getRawApiError());
+             Assertions.assertEquals("Transaction id not found.", e.getApiErrorMessage());
+             return;
+         }
+         Assertions.fail();
+     }
+
     public AppStoreServerAPIClient getClientWithBody(String path, Consumer<Request> requestVerifier) throws IOException {
         String body = TestingUtility.readFile(path);
         return getAppStoreServerAPIClient(body, requestVerifier);

src/test/resources/models/appTransactionDoesNotExistError.json

@@ -0,0 +1,4 @@
+{
+   "errorCode": 4040019,
+   "errorMessage": "No AppTransaction exists for the customer."
+}

src/test/resources/models/appTransactionInfoResponse.json

@@ -0,0 +1,3 @@
+{
+   "signedAppTransactionInfo": "signed_app_transaction_info_value"
+}

src/test/resources/models/invalidTransactionIdError.json

@@ -0,0 +1,4 @@
+{
+   "errorCode": 4000006,
+   "errorMessage": "Invalid transaction id."
+}

src/test/resources/models/transactionIdNotFoundError.json

@@ -0,0 +1,4 @@
+{
+   "errorCode": 4040010,
+   "errorMessage": "Transaction id not found."
+}