diff --git a/app/routes/envios.py b/app/routes/envios.py
index 7205cbb..4120cd8 100644
--- a/app/routes/envios.py
+++ b/app/routes/envios.py
@@ -83,13 +83,24 @@ async def erp_sync_diagnosticos(user: dict = Depends(get_current_user)):
                 lote = diagnosticos[i:i + batch_size]
                 try:
                     resp = await client.post(url, json={"rows": lote}, headers=headers)
-                    data = resp.json()
+                    try:
+                        data = resp.json()
+                    except Exception:
+                        raw = resp.text[:400].strip()
+                        errores.append(f"Lote {i}-{i+len(lote)} HTTP {resp.status_code}: {raw!r}")
+                        if i == 0:
+                            break  # Si el primer lote ya falla, no tiene sentido continuar
+                        continue
                     if data.get("ok"):
                         insertados += data.get("insertados", len(lote))
                     else:
                         errores.append(f"Lote {i}-{i+len(lote)}: {data.get('error', '?')}")
+                        if i == 0:
+                            break
                 except Exception as ex:
                     errores.append(f"Lote {i}-{i+len(lote)}: {ex}")
+                    if i == 0:
+                        break
 
         return JSONResponse({
             "ok":        len(errores) == 0,