Hi @Juani_Gnacio,
Based on the error message, the issue is related to CORS.
Just to be sure if it’s CORS or not, can you change your logic to integrate CORS without custom configs, and check if that would work:
app.use(cors());
I am not a Vercel expert, but it’s also possible that something has to be configured on the Vercel level for CORS to run properly.
Other than that, your backend code seems valid.