Set up completion codes.

A panel study is a loop with three URLs. First, the study URL: the link you paste into Prolific, pointing at your survey, with placeholders that Prolific fills in per participant:

https://yoursurvey.example/s/abc123
    ?PROLIFIC_PID={{%PROLIFIC_PID%}}
    &STUDY_ID={{%STUDY_ID%}}
    &SESSION_ID={{%SESSION_ID%}}

When participant 5f8a… clicks it, Prolific replaces the {{%…%}} placeholders with their IDs. Save those parameters with the response so you can match it to the panel submission.

Second, the completion URL: where you send participants when they finish. Prolific gives you this on the study page; it looks like https://app.prolific.com/submissions/complete?cc=A1B2C3D4. Redirecting there marks the submission complete automatically.

Third, the screen-out route uses a separate code. See Logic and branching in the help center.

A redirect returns participants to Prolific after submission. They may still close the tab early or have navigation blocked, so also print the code on the thank-you screen, so anyone who missed the redirect can paste it into Prolific manually.

Check that your ending includes a code or redirect. Without either, a participant may need your help to confirm completion.

In Plumeform both halves are one settings panel: set the completion code and paste the redirect URL, and the thank-you screen shows the code and forwards automatically. The share panel's launch kit generates the study URL with the placeholders already wired.

If you screen for eligibility, configure a separate ending for people who do not qualify. Prolific studies can use multiple completion codes with different outcomes, including separate codes for completion and screening exits. Match each survey ending to the code configured in your panel study.

Your survey tool therefore needs two endings: the thank-you screen (completion code + redirect) and a separate screen-out screen with its own code and its own redirect. The screen-out copy matters more than people think — “you didn't qualify” reads as an accusation; “this study needs a specific group and this one isn't a match — your time is still appreciated” reads as respect. You will meet these participants again in your next sample.

Put the screener in the first minute. The earlier someone screens out, the cheaper it is for you and the fairer it feels to them.

Never launch a panel study without one dry run of the full loop. Open your own study URL with fake parameters — say ?PROLIFIC_PID=TEST123 — and complete the survey. Check three things: the response stored your test ID, the thank-you screen shows the right code, and the redirect lands on Prolific's completion page (it will refuse your fake session, which is fine — you only care that you arrived). Then check the screen-out path the same way by answering as an ineligible participant.

The catch: that dry run is now a row in your data. Either delete it by hand before launch, or use a tool with a real test mode — Plumeform treats any link opened with ?test=1 as a dry run: flagged, excluded from results and quotas, and deletable in one click. Your rehearsals never touch your dataset.