Passwordless SMS and email not sending reliably

We’re using the passwordless.sendSMS and passwordless.sendEmail methods to send codes from a Node server, and it works very unreliably. Locally it works for a while, and stops working. Deployed to Vercel it almost never works.

We can consistently get I to work with new emails and new phone numbers, but existing Auth0 users sometimes get codes.

No errors are returned from the methods themselves, Auth0 logs or Twilio logs. In fact the Auth0 logs don’t show anything: no errors, not sent code logs, nothing.

I don’t think we’re hitting any rate limits as we are only testing this amongst max 4 people.

We’ve checked all we can check both on Auth0 and our code, but are really at loss here. Very hard to figure out since it works sometimes, and no errors to be found.

Any ideas of what this could be?