Each study has a limited number of spaces available for participants, which is set by the researcher. Once all spaces have been filled, the study will disappear from your studies list. Due to Prolific's large participant pool, study spaces can fill up quickly—sometimes by the time you click "Take part." Studies appear to all eligible participants, so multiple people may be attempting to secure a space simultaneously.
If you're unable to secure a space, you'll see a message indicating that no spaces are available, even if spaces were shown as available just seconds before. This error is often labeled as "The study you are trying to access is no longer in progress," which can occur due to high demand or simultaneous access by multiple participants.
If a study appears with one space available, this often occurs when a participant returns their place, reopening the last space.
In some cases, a researcher may pause a study to fix an issue. This may prevent you from entering the study despite places showing as available. If this happens, the study should disappear when you refresh your page. Additionally, you can dismiss the study from your dashboard to clear unavailable studies and monitor for updates if the study is relisted by the researcher.
If the issue persists, consider noting the study name or ID and contacting Prolific support for further assistance. As an optional step, you may block researchers whose studies frequently appear but are unavailable to stop receiving their studies.