REDCap.

1 · Pass the Samply IDs into the survey

URL pre-fill into hidden Text Box fields whose Variable Names match the query-string keys (@HIDDEN). The value is stored because the field is on the submitted instrument.

1. In Online Designer, on the FIRST survey instrument, add Text Box fields with Variable Names exactly matching the incoming keys (e.g. messageid, samply_id, participant_code — case-sensitive, no dashes/colons).
2. In each field's "Action Tags / Field Annotation" box add @HIDDEN (or @HIDDEN-SURVEY) so participants do not see it.
3. Configure the start link so its query keys equal those variable names. REDCap pre-fills and stores them with the response.
4. Test: complete a survey via a link with sample values and confirm the export contains the fields.

2 · Register completion

Survey Settings → Survey Termination Options → "Redirect to a URL", piping the stored field as [messageid].

1. Make sure messageid was captured into a stored Text Box field (see above).
2. On the LAST instrument, open Survey Settings → Survey Termination Options and select "Redirect to a URL".
3. Enter: https://samply.uni-konstanz.de/studies/<study-slug>/done/[messageid] — REDCap replaces [messageid] with the stored value at submission.
4. Save and test end-to-end.

Reserved parameters & gotchas

Avoid REDCap's own params (s, __response_hash__). Variable names are case-sensitive, no dashes/colons. CRITICAL: the value is only saved when the instrument holding the field is submitted — keep the hidden fields on the first instrument.

Things to watch out for

• "Redirect to a URL" cannot be combined with "Survey Completion Text".
• Piping into the redirect works for all field types except checkboxes — use a Text Box for messageid.

Sources

These steps were verified against the platform's official documentation.

• https://www.sona-systems.com/help/redcap/
• https://help.redcap.ualberta.ca/help-and-faq/survey-parameters
• https://www.iths.org/news/redcap-tip/redcap-tip-of-the-month-survey-termination-options/