There are two possibilities for other users with a purchased subscription to edit a plan you created:
1. If they are part of your team with a subscription assigned, they are editors by default and can edit and save the files created by other editor team members in your team, as long as the project is not part of a division the user has no access to.
2. If they are not part of your team and have a separate subscription purchased, you can share the project you created with them by going to menu Share – Share – Share as MPP. The user outside of your team will be able to open the shared project you created and edit it using their subscription. Please note that if they are not part of your team, they will not have rights to overwrite the original file. They will have to save it to their local device or to a Cloud location.