No preview / debug mode available

Hi, we have setup tag manager in an existing matomo development installation.
I can publish tags with success: they are working and collecting data.
Thank you for this very nice feature!

But I can not see or work with the preview function of the tag manager.
I also tried it in other browsers with appended ?mtmPreviewMode=CONTAINERID and &mtmPreviewMode=CONTAINERID.

Our Websites and the matomo installation have different URLs:
piwik-dev.ourwebsite vs. develop.ourwebsite
develop.ourwebsite is password protected in an simple manner.

Do you have any ideas how I can get the preview to work?


Did you at first enable the preview in Matomo?

Do you see any errors in the developer tools of your browser?


to be honest: I am the user of our matomo, not the admin …
Since tag manager seems to be meant for people like me, I gave it a try.

Did we enable the preview?
Within tag manager: yes. Matomo in general? no idea.

Yes, I get piwik.js:63 Uncaught Error: A siteId must be given to add a new tracker in our pre existing matomo (piwik.js) file.
Site ID is set to 1 and should be ok.

If I am too clueless, I can wait till admin returns from vacation …