Due to the way CloudResearch's system is setup, you can incur a negative Lab Balance if you launch multiple MTurk Toolkit studies within close succession of each other and do not have enough Lab funds to cover the cost of both studies.
During the day, CloudResearch records participants that are approved for your MTurk Toolkit studies and what charges you incur. Then, at the end of the day, money is withdrawn from your Lab Balance. This method of accounting can sometimes lead to a negative Lab Balance if you launch multiple MTurk Toolkit studies within close succession of each other and do not have enough money in your account to cover the cost of both studies.
Example
Imagine you have $20 in your CloudResearch Lab Balance. If you launch an MTurk Toolkit study that will cost you $12 in Lab Fees, the $12 is not removed from your Lab Balance right away. Instead, money is withdrawn at the end of each day, based on the fees incurred throughout the day, until your study is complete. Thus, if you decided shortly after launching your first study to launch a second study that would cost you $10 in Lab Fees, CloudResearch would allow you to launch the second study even though there is not enough money in your account to cover the total Lab Fees you could incur for both studies. We allow you to launch the second study because it is not a guarantee that you will pay all the money estimated as the Lab Fees for your studies. If you ended a study early or failed to recruit all the participants in your sample, your Lab Fees would be lower.
When it's possible for you to incur a negative Lab Balance by launching multiple studies, CloudResearch does not stop live studies or prevent you from launching an additional study. Instead, we will post a negative lab balance that will have to be paid before you can launch additional studies.