Plan requirement
Custom variables and Automatic Redirect both require a paid QuestionPro plan — the round-trip does not work on the free version.
1 · Pass the Samply IDs into the survey
custom1–custom255 (or ext_ref) are captured automatically from the URL — no in-survey field needed — and appear in the export.
- Build the start link so the collector receives %MESSAGE_ID% in a custom variable, e.g. ?custom1=%MESSAGE_ID%&custom2=%SAMPLY_ID%.
- Paste this as the Samply start link; QuestionPro captures custom1/custom2 automatically.
- Optionally label the variable under Custom Variables settings for readable data.
- Verify in Response Viewer and the Excel/CSV export that custom1 holds the value.
Example start link
https://www.questionpro.com/t/<collectorID>?custom1=%MESSAGE_ID%&custom2=%SAMPLY_ID%
2 · Register completion
Finish Options → Advanced Options → Automatic Redirect → Website Address, piping the stored variable as ${custom1}.
- Ensure the message id arrived as a custom variable (e.g. custom1).
- Survey → Edit → Finish Options → Advanced Options → Automatic Redirect.
- In "Website Address" enter: https://samply.uni-konstanz.de/studies/<study-slug>/done/${custom1}.
- Save; QuestionPro substitutes ${custom1} with the real message id at the end and redirects. Test end-to-end.
Example completion redirect
https://samply.uni-konstanz.de/studies/<study-slug>/done/${custom1}
Reserved parameters & gotchas
Reserved names: customN, ext_ref, email. Values may not contain comma or hash. Prefer ${custom1} over ${ext_ref} in the redirect — only ${custom1}–${custom255} are documented piping tags.
Things to watch out for
- ext_ref capture works too, but using ${ext_ref} inside the redirect is undocumented — stick to ${custom1} for the round-trip.
Sources
These steps were verified against the platform's official documentation.