In order to add participants to a live study, select the option to "Increase places" from the blue Action menu.
The number you enter here should be the total number of places you want to be available for your study after increasing places, and not the number you want to increase by. The study's pricing will automatically re-calculate when you do this.
Once the additional places have been added, the study will automatically become active. You will need to refresh the page to see the correct study status.
You can also increase places for a Completed study in exactly the same manner. When you have increased places, the study will be moved from your "Completed" studies folder back into the "Active" one, and data collection shall resume.
If you have insufficient funds to increase places on a study, this may be explained by a discrepancy between your total and available balance. You can read more about this here: Total and Available Balance.