I have a user picker that selects max 3 users. In the process model I want to send the email to all the users in the array of users.
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Can you share what you've already tried and what difficulty you're having? In general (assuming a valid array of users with valid email addresses) this is usually pretty straight forward, IIRC, because you can just target your user array in the "to:" field of the Send Email node.
toemailaddress(pv!reportRequest.reviewer)and the reviewer variable just has the array of users with valid email addresses
If pv!reportRequest.reviewer is user type, I don't think you even need to wrap it in toEmailAddress(). That function seems to only be needed when you want to target plaintext email addresses as recipients. In fact it might be hurting you here, because if you wrap an array of user in this function, it might accidentally be trying to treat their usernames as email addresses, which would definitely not work. But again I'm not sure since you haven't actually said what's working / not working.