Hi @Marie Sciberras,
Thank you for your question! It sounds like you were on the right track, but I’d be happy to clarify.
If you are currently on the Starter plan and paying for your own license, please note that when you invite other users via email to collaborate as editors, they are added as paid members of your team. This is why you received a message about additional charges after the trial period ends.
To avoid increasing your subscription cost, you can instead invite these collaborators as Visitors. Visitors can edit the board without being added as team members or requiring a paid seat. Simply share the board link with them and set the access settings to allow Visitors to edit. Learn more here: https://help.miro.com/hc/en-us/articles/360012524559-Collaboration-with-Visitors.
Please let me know if you need further assistance.