Merging User Identities in Mixpanel's Simplified Merge API

Hi. Is there a robust way to merge identities in simplified merge API ? We have a mixpanel project with Simplified Merge API. And the following scenario case: - application with users - there is a trial period for users - the trial (app) and the main one have different identification systems for users - (the former based on user email and the latter identified by user ID) - (so the databases are different) - (for historical / technical reasons) - how do we currently manage the tracking identification - after trial users sign up, we track them by email - (so we call identify with user_id based on email) - when trial user is converted, we track them by user ID (from database) - (so we call `identify` with `user_id` based on database user record ID) However, the events from two (apps / systems) aren't linked together. (Looks like Identity Failure Reason: errAnonDistinctIdAssignedAlready error is a mixpanel indicator for a problem). So, the question is the following: is there any robust way in mixpanel simplified merge API to merge two identities from different systems ?