diff --git a/src/test/java/com/adyen/TerminalCloudAPITest.java b/src/test/java/com/adyen/TerminalCloudAPITest.java
index fe86ea561..005a5e3d4 100644
--- a/src/test/java/com/adyen/TerminalCloudAPITest.java
+++ b/src/test/java/com/adyen/TerminalCloudAPITest.java
@@ -38,11 +38,13 @@
 import com.adyen.model.nexo.PaymentReceipt;
 import com.adyen.model.nexo.PaymentRequest;
 import com.adyen.model.nexo.PaymentResult;
+import com.adyen.model.nexo.PaymentTransaction;
 import com.adyen.model.nexo.Response;
 import com.adyen.model.nexo.ResultType;
 import com.adyen.model.nexo.SaleData;
 import com.adyen.model.nexo.SaleToPOIRequest;
 import com.adyen.model.nexo.SaleToPOIResponse;
+import com.adyen.model.nexo.TransactionConditions;
 import com.adyen.model.terminal.SaleToAcquirerData;
 import com.adyen.model.terminal.TerminalAPIRequest;
 import com.adyen.model.terminal.TerminalAPIResponse;
@@ -299,6 +301,50 @@ public void syncInputRequestSuccess() throws Exception {
     assertFalse(requestAsJson.contains(": null"), "Found null value");
   }
 
+  /**
+   *
+   * <p>When {@code setDebitPreferredFlag} is never called, the backing field stays {@code null} and
+   * Gson must omit it from the serialized JSON entirely. This allows the terminal to choose the
+   * payment type freely (DEBIT, CREDIT, or VOUCHER) rather than being forced to CREDIT by a
+   * spurious {@code "DebitPreferredFlag": false}.
+   */
+  @Test
+  public void debitPreferredFlagOmittedFromJsonWhenNotSet() throws Exception {
+    Client client = createMockClientFromFile("mocks/terminal-api/payment-async-success");
+    TerminalCloudAPI terminalCloudApi = new TerminalCloudAPI(client);
+
+    TerminalAPIRequest terminalAPIRequest = createTerminalAPIPaymentRequest();
+
+    TransactionConditions transactionConditions = new TransactionConditions();
+    // Deliberately do NOT call transactionConditions.setDebitPreferredFlag(...)
+
+    PaymentTransaction paymentTransaction = new PaymentTransaction();
+    paymentTransaction.setTransactionConditions(transactionConditions);
+
+    terminalAPIRequest
+        .getSaleToPOIRequest()
+        .getPaymentRequest()
+        .setPaymentTransaction(paymentTransaction);
+
+    terminalCloudApi.async(terminalAPIRequest);
+
+    final ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
+    verify(client.getHttpClient())
+        .request(
+            isNotNull(),
+            captor.capture(),
+            any(com.adyen.Config.class),
+            eq(true),
+            isNull(),
+            eq(ApiConstants.HttpMethod.POST),
+            isNull());
+
+    String requestAsJson = captor.getValue();
+    assertFalse(
+        requestAsJson.contains("DebitPreferredFlag"),
+        "DebitPreferredFlag must be absent from JSON when setter is never called");
+  }
+
   /** Mocked response for stored value type for POST /sync */
   @Test
   public void syncPaymentRequestStoredValueSuccess() throws Exception {
diff --git a/src/test/java/com/adyen/TerminalLocalAPITest.java b/src/test/java/com/adyen/TerminalLocalAPITest.java
index f63a85032..a09e5e6fe 100644
--- a/src/test/java/com/adyen/TerminalLocalAPITest.java
+++ b/src/test/java/com/adyen/TerminalLocalAPITest.java
@@ -32,14 +32,18 @@
 import com.adyen.model.nexo.PaymentInstrumentType;
 import com.adyen.model.nexo.PaymentReceipt;
 import com.adyen.model.nexo.PaymentResult;
+import com.adyen.model.nexo.PaymentTransaction;
 import com.adyen.model.nexo.Response;
 import com.adyen.model.nexo.ResultType;
 import com.adyen.model.nexo.SaleData;
 import com.adyen.model.nexo.SaleToPOIResponse;
+import com.adyen.model.nexo.TransactionConditions;
 import com.adyen.model.terminal.TerminalAPIRequest;
 import com.adyen.model.terminal.TerminalAPIResponse;
 import com.adyen.model.terminal.security.SecurityKey;
 import com.adyen.service.TerminalLocalAPI;
+import com.adyen.terminal.serialization.TerminalAPIGsonBuilder;
+import com.google.gson.Gson;
 import java.math.BigDecimal;
 import java.util.List;
 import org.junit.jupiter.api.Test;
@@ -135,6 +139,38 @@ public void syncPaymentRequestSuccess() throws Exception {
     assertEquals(BigDecimal.ONE, paymentResult.getAmountsResp().getAuthorizedAmount());
   }
 
+  /**
+   * Regression test for the DebitPreferredFlag workaround (Option A) on the local Terminal API.
+   *
+   * <p>{@link TerminalLocalAPI} serializes the request with {@link TerminalAPIGsonBuilder} before
+   * encrypting it. When {@code setDebitPreferredFlag} is never called, the backing field stays
+   * {@code null} and Gson must omit it from the JSON, allowing the terminal to choose the payment
+   * type freely (DEBIT, CREDIT, or VOUCHER).
+   */
+  @Test
+  public void debitPreferredFlagOmittedFromJsonWhenNotSet() throws Exception {
+    Gson gson = TerminalAPIGsonBuilder.create();
+
+    TerminalAPIRequest terminalAPIRequest = createTerminalAPIPaymentRequest();
+
+    TransactionConditions transactionConditions = new TransactionConditions();
+    // Deliberately do NOT call transactionConditions.setDebitPreferredFlag(...)
+
+    PaymentTransaction paymentTransaction = new PaymentTransaction();
+    paymentTransaction.setTransactionConditions(transactionConditions);
+
+    terminalAPIRequest
+        .getSaleToPOIRequest()
+        .getPaymentRequest()
+        .setPaymentTransaction(paymentTransaction);
+
+    String json = gson.toJson(terminalAPIRequest);
+
+    assertFalse(
+        json.contains("DebitPreferredFlag"),
+        "DebitPreferredFlag must be absent from JSON when setter is never called");
+  }
+
   /** Test success flow for local request that includes unexpected attributes */
   @Test
   public void syncPaymentRequestSuccessWithAdditionalAttributes() throws Exception {