Unable to create/update fields: "x". Please check the security settings of this field and verify that it is read/write for your profile or permission set.

This error means that the user you have connected the migration with does not have access to edit the field named. Please review the permission set/profile of the user and ensure there is access to read/write fields. We also recommend to check the settings on the field itself to ensure it is also set to be able to be edited.