Languauge interpretation

Hi there, I am tech hosting a large event for a client.

The client has a Business account and large meetings (500 attendees) and webinar features.
The language interpretation in the account settings of the client is turned on.

All interpreters have given their e-mail addresses which was used when creating their Zoom accounts and they join from laptop/computer from the Zoom app.
However, even though the e-mail addresses were programmed in the Zoom meeting link and the interpreters joined from the link in the invitation e-mail.... However when the interpreters joined the meeting in the tech dry run none of the translators were recognized so I had to manually assign all 20+ interpreters. So even when I as a host want to start the interpretation the pre-assigned list does not work. 

This is troublesome for the day of the event, what am I missing and how can I make the pre-assign list work?

Thank you in advance.

Warmly,

Sara