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?

Hi,

Did you at first enable the preview in Matomo?

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

Hi,

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.

Errors:
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 …