What happen when I changed the plan paid to free?

@Vinci - Here are a few additional notes.

Only three boards will be editable

As noted in the Free Plan help center article – and likely your biggest limitation – once on the Free Plan, only the three most recently created Miro boards will be editable for any users on the team – again, this limit is for the entire team, and does not mean that each user will get three boards they can edit. So, for example, you have 100 boards in your paid plan now, once you downgrade to free, you can only edit the last three boards that were created.

Locked boards

Another thing to note is, once you downgrade to free, some boards may shows “LOCKED” and will need to be unlocked by changing the team-level share setting from “No access” to Edit, View, or Comment. More on this here.

No Visitor access

While this would be addressed in @ElvaMiro‘s links, is worth mentioned on its own that the Free Plan does not support the Visitors feature, i.e., you will not be able to quickly set the “Anyone with the link” to “Can edit” and have a non-team member be able to edit your boards. Only full team members can edit boards that reside in a Free Plan. More on the visitors feature here.

Furthermore, once they are full members, then can see all boards in your team and even create boards – this is because the Free Plan does also not support making boards private - more on private boards here.