diff --git a/sync-service/src/main/java/com/teterialosjuanjos/tfg/sync_service/integration/prestashop/PrestashopClient.java b/sync-service/src/main/java/com/teterialosjuanjos/tfg/sync_service/integration/prestashop/PrestashopClient.java
index 960acb8..e91997f 100644
--- a/sync-service/src/main/java/com/teterialosjuanjos/tfg/sync_service/integration/prestashop/PrestashopClient.java
+++ b/sync-service/src/main/java/com/teterialosjuanjos/tfg/sync_service/integration/prestashop/PrestashopClient.java
@@ -4,6 +4,7 @@ import com.teterialosjuanjos.tfg.sync_service.config.IntegrationProperties;
 import com.teterialosjuanjos.tfg.sync_service.integration.prestashop.dto.*;
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.beans.factory.annotation.Qualifier;
+import org.springframework.http.MediaType;
 import org.springframework.stereotype.Component;
 import org.springframework.web.client.RestClient;
 
@@ -84,6 +85,7 @@ public class PrestashopClient {
 
     /**
      * Creates a new product in PrestaShop.
+     * PS WebService requires XML request body even when {@code output_format=JSON} is set.
      *
      * @return the created product including its assigned {@code id}
      */
@@ -94,7 +96,8 @@ public class PrestashopClient {
                         .queryParam("ws_key", wsKey)
                         .queryParam("output_format", "JSON")
                         .build())
-                .body(new PrestashopProductDto.SingleResponse(dto))
+                .contentType(MediaType.APPLICATION_XML)
+                .body(toProductXml(dto))
                 .retrieve()
                 .body(PrestashopProductDto.SingleResponse.class);
 
@@ -109,7 +112,8 @@ public class PrestashopClient {
                         .queryParam("ws_key", wsKey)
                         .queryParam("output_format", "JSON")
                         .build(id))
-                .body(new PrestashopProductDto.SingleResponse(dto))
+                .contentType(MediaType.APPLICATION_XML)
+                .body(toProductXml(dto))
                 .retrieve()
                 .toBodilessEntity();
     }
@@ -147,7 +151,8 @@ public class PrestashopClient {
                         .queryParam("ws_key", wsKey)
                         .queryParam("output_format", "JSON")
                         .build(id))
-                .body(new PrestashopStockAvailableDto.SingleResponse(dto))
+                .contentType(MediaType.APPLICATION_XML)
+                .body(toStockAvailableXml(dto))
                 .retrieve()
                 .toBodilessEntity();
     }
@@ -194,4 +199,80 @@ public class PrestashopClient {
                 .body(PrestashopCustomerDto.SingleResponse.class);
         return response != null ? response.customer() : null;
     }
+
+    // ── XML builders ──────────────────────────────────────────────────────
+    // PS WebService requires XML body for writes; output_format=JSON only affects the response.
+
+    private String toProductXml(PrestashopProductDto dto) {
+        String name = firstLangValue(dto.name());
+        String description = firstLangValue(dto.description());
+        String descShort = firstLangValue(dto.descriptionShort());
+        String slug = toSlug(dto.reference());
+
+        StringBuilder sb = new StringBuilder(512);
+        sb.append("<?xml version=\"1.0\" encoding=\"UTF-8\"?>");
+        sb.append("<prestashop xmlns:xlink=\"http://www.w3.org/1999/xlink\">");
+        sb.append("<product>");
+        if (dto.id() != null) {
+            sb.append("<id>").append(dto.id()).append("</id>");
+        }
+        sb.append("<reference>").append(escapeXml(dto.reference())).append("</reference>");
+        if (dto.price() != null) {
+            sb.append("<price>").append(escapeXml(dto.price())).append("</price>");
+        }
+        if (dto.active() != null) {
+            sb.append("<active>").append(escapeXml(dto.active())).append("</active>");
+        }
+        if (dto.idCategoryDefault() != null) {
+            sb.append("<id_category_default>").append(escapeXml(dto.idCategoryDefault())).append("</id_category_default>");
+        }
+        sb.append("<id_tax_rules_group>1</id_tax_rules_group>");
+        sb.append("<link_rewrite><language id=\"1\">").append(escapeXml(slug)).append("</language></link_rewrite>");
+        sb.append("<name><language id=\"1\">").append(escapeXml(name)).append("</language></name>");
+        sb.append("<description><language id=\"1\">").append(escapeXml(description)).append("</language></description>");
+        sb.append("<description_short><language id=\"1\">").append(escapeXml(descShort)).append("</language></description_short>");
+        sb.append("</product>");
+        sb.append("</prestashop>");
+        return sb.toString();
+    }
+
+    private String toStockAvailableXml(PrestashopStockAvailableDto dto) {
+        StringBuilder sb = new StringBuilder(256);
+        sb.append("<?xml version=\"1.0\" encoding=\"UTF-8\"?>");
+        sb.append("<prestashop xmlns:xlink=\"http://www.w3.org/1999/xlink\">");
+        sb.append("<stock_available>");
+        if (dto.id() != null) {
+            sb.append("<id>").append(dto.id()).append("</id>");
+        }
+        if (dto.idProduct() != null) {
+            sb.append("<id_product>").append(dto.idProduct()).append("</id_product>");
+        }
+        String idAttr = dto.idProductAttribute() != null ? dto.idProductAttribute() : "0";
+        sb.append("<id_product_attribute>").append(idAttr).append("</id_product_attribute>");
+        sb.append("<quantity>").append(dto.quantity()).append("</quantity>");
+        sb.append("</stock_available>");
+        sb.append("</prestashop>");
+        return sb.toString();
+    }
+
+    private static String firstLangValue(List<PrestashopProductDto.LangValue> langs) {
+        if (langs == null || langs.isEmpty()) return "";
+        String v = langs.get(0).value();
+        return v != null ? v : "";
+    }
+
+    /** Generates a URL-safe slug from any string (used for PS link_rewrite). */
+    private static String toSlug(String text) {
+        if (text == null || text.isBlank()) return "product";
+        return text.toLowerCase().replaceAll("[^a-z0-9]+", "-").replaceAll("^-|-$", "");
+    }
+
+    private static String escapeXml(String text) {
+        if (text == null) return "";
+        return text.replace("&", "&amp;")
+                   .replace("<", "&lt;")
+                   .replace(">", "&gt;")
+                   .replace("\"", "&quot;")
+                   .replace("'", "&apos;");
+    }
 }