I have a backup of open project project, how to upload it to the free instance that you host for 14 days for free for every interested participant?

Hello Michał,

restoring a backup into a cloud instance can only be done by the OpenProject team currently. I kindly ask you to reach out via support@openproject.com (please include your trial domain (yourdomain.openproject.com) to get more information on this.

Best

Alexander