Tvheadend doesn't work

I try to get tvheadend running. I did everything that was needed and I can now access the webinterface and my adapter is correctly installed. But tvheadend can’t find it. In the wiki of tvheadend they say:

In order for Tvheadend to control video adapters on the system it must
be granted access to those devices. Most systems have a ‘video’ group
with write access to the video adapter devices. When Tvheadend is
started as a daemon (if Tvheadend is installed from a distribution
package this is most likely the way it is) it will change its primary
group to ‘video’ in order to access these groups. If your system is
configured in a different way you can either change the group membership
of the video adapters (/dev/dvb, etc) or reconfigure the Tvheadend
start up parameters.

I use the default osmc user and have no idea how I grant tvheadend now access. Does anybody have an idea?

Are you using the version of Tvheadend from the App Store? If so, I suggest you try the version recommended by HarryL here: OSMC RC Unable to install TVHEADEND - #13 by EMJB.

No, I installed the one from the tvheadend wiki. (3.4)

@trolbox - Suggest you try HarryL’s version.

I did. Still no access. Using it on OpenELEC without problems.

I found that I needed to include both amendments made by HarryL to his post to get the scan to work.