[BUG] Azure B2C calls a RestAPI endpoint defined in custom policy multiple times.

Question

We have a OrchestrationStep at the end of signup UserJorney in custom policy that calls a Rest Endpoint to send out a signup email.
Azure calls our Rest endpoint multiple times causing it to send out more than one signup email.
This does not always happen, but happens most of times. Sometimes, it calls 2~4 times, but sometimes it calls hundred times.
One of our customer reported that he/she received 600 signup emails!
We have a logging infra that monitors http requests/responses, and we confirm that Azure is actually calling our endpoint multiple times for an email address at the end of signup.

This is serious since our new customers basically receives massive number of emails when they sign up our service.