After starting a Teams Meeting it is possible to add participants as follows:

1. Click on 'Invite someone or dial a number'

2. Search for the person you want to add (tip: the best way to search is by the person's last name without prefix)

3. Click 'Request to join'

The person will automatically receive a notification asking to join the Meeting. This must be accepted by the person himself, and will be added automatically after this.