A Prosal becomes inactive when it is past its submission deadline. This means that the Prosal does not display on the marketplace and it cannot receive new responses.
A Prosal can be made active again by changing the submission deadline.
To do so, visit the Inactive Prosals tab in the Dashboard and click on the Prosal you would like to set to Active. Then click Edit Prosal and edit the submission deadline to be past the current date. The Prosal will become inactive again once it's past the updated submission deadline.
The new deadline and edit will be recorded in the Public Questions section of your View Prosal page.